I started !programming.dev because I am a moderator of several 100k+ subs over on Reddit and I didn't want my communities to not have a place to go if Reddit crashed and burned (even though it's incredibly unlikely). The main sub I moderated (/r/ExperiencedDevs) for years wanted user verification to combat the spam that was newbies commenting and posting about things they didn't really know or understand. This will be possible to actually implement on Lemmy, whereas reddit was closed source, and didn't really care about their communities.
I am also a strong supporter of pulling control away from megacorps. We need more small to medium sized businesses on the planet.
For selfish reasons? I wanted to work on something new and have true ownership over it, the ability to build a community that worked together to build something without capitalism standing in the way. It might seem strange, but one of the first things I did was bring multiple other people on board to help me maintain the server, even going so far as to add domain managers to the domain name. This was all to counter the major questions people were asking around "what if the host decides they don't want to host anymore?". Well hopefully the programming.dev community is willing to take that burden if the time ever comes, even though I hope it doesn't. I also wanted to start something similar to a coop, where ownership is shared, meaning users have incentives to make the platform better. I have lots of ideas around this, but this will never be possible on Reddit. It is quite feasible here.
I also had the chance to buy an incredibly dope domain name! https://programming.dev! Why wouldn't I jump at that chance? And I get to even use it instead of let it flounder. So many reasons to host something like this, to build a trusting community, a safe space to have to let people talk about a shared love/topic/hobby.