You may find thousands reason to self-host or not but my personal main reason is... just for fun.
It's very interesting to understand how the web works and become not just a user but a creator and owner. So one of the main my goals is to make teaching videos and tutorials for regular people about how to make a website. This may be a good hobby for many people. They may even don't use this or any other product but create something for themselves.
If you love some dish you may want to learn which ingredients are used and try to cook it yourself and enjoy by the process and result. But even if you aren't interested in cooking you anyway should have a right to know which ingredients were used and even count calories.
In the modern web you are using someone's sites but you don't know what exactly happens inside. They may use dark patterns to exploit your human habits that you don't even know. They also may sell your data to some 3rd parties. Did you ever receive a spam letter? That happened because someone sold your email address.
This may sound like not a big problem but you just don't and can't realize how important it is. Especially the problem become more dramatic when a service has some recommendation algorithm that may affect peoples perception. Some big companies published details about it like Twitter. The problem is that now bad peoples may also learn how to cheat it. It looks like there is no a good solution for this but you must at least clearly understand that it's always have some algorithm and this is important.
I finally realized that I must self-host my things when Google shut down their RSS Blogs Reader that I loved and millions of other people too. They forced everyone to move to Google Plus social network which can't be used to just read someone's RSS blog. And then they closed it ether and many people moved to the Facebook which is full of dark patterns. The Google have killed so many of their products that there is even a graveyard of them.
Instapaper developer Marco Arment speculated that the real reason for the closure was to try to keep everyone reading and sharing information using the now defunct Google+, and that it signaled the end of the era of unrestricted and interoperable web services like RSS from large organizations like Google, Facebook, and Twitter.
Yep, this is exactly what happened. Today not so many people even remember now how the tech giants gain their power by destroying independent authors.
I started using an RSS reader in the Firefox browser but it wasn't convenient. The Firefox team didn't work on the feature which was probably the most important but eventually just removed the RSS reader at all. Anyway, at that moment most interesting authors moved to social networks. We just left with nothing to read.
Similarly, the Firefox ancestor Netscape had an easy-to-use built-in mail client but they removed it so many users moved to Gmail and other big mail providers. And today this big mail providers are basically blocking mail from independent mail servers so the decentralized web again become fully controlled. The Email is essential for internet and you can't even register anywhere without it. That's why this is one of the main goals of the project to bring personal mail servers to people.
This all not just an unfair competition but also creates many risks for small businesses. Big companies can afford top level programmers, marketers, lawyers and lobbyist and this leads to the Matthew effect of accumulated advantage: the rich get richer and the poor get poorer. This was especially clear seen during the recent (and not last!) pandemic: many small retail shops and services got bankrupt while big marketplaces like Amazon become even more bigger.
Don't get me wrong: big companies making a lot of good and they are really needed. They made possible to have a good discussions in internet and fighting with bots, hackers and unfair censorship. The only thing that I see is that middle and small sized companies are loosing but they are also important because they can provide the best specialized value to customers.
In the nature you have a forest where you have tall tries but also some bushes and grass. You may have elephants and ants and they all form one ecosystem. And that's this project about: I wish to make a grass for internet with some footpath on it for your pleasant walk. Small websites but with some search engine on them, aggregators and recommendation system. But not even trying to become a big trie.
It also gives you a good old feeling of owning something. Owning of your place in internet. Previously social networks gave this feeling to millions of people but they don't really own their profile and once they get blocked they just shocked.
My buddy makes furniture and sells on Instagram. He is nervous about this because if he lost its account he will no many to feed his family. He asked me to make him a website but it was shocked when I said how much it will cost. Instead, as I recommend, he made a website on some website constructor and that made him more calm. He had only one sale from the website He said that it anyway would prefer to have own site and become independent and safe.
And, you see, I can recommend him to buy some domain, hosting, install WordPress but it still too complicated and remains dependencies to a hosting.
In my world view this should but just as easy like: open your computer, click on some checkbox Enable site, select template and then type what you want.
You already should have a website at home, but you can just not use it.
It like accessories e.g. a paper and pen: everybody have them at home and once in a year you will use them.
Similarly, once you need to quickly share photos you can just remember that you can do that right here.
Most of the selfhosting solutions today have a focus on privacy, security, reducing risk or customization. Some are focused on fighting on "surveillance capitalism". But the Yurt project have a focus on making more widespread simple utility product.