It’s non profit by default, the very thing that social media needs.
People who run Lemmy servers do it at their own cost. That’s not to say they can’t run ads or choose other ways to become profitable. The big difference between a lemmy instance and something like Reddit is that anyone can start a new instance if the current one goes to shit. If the admins do something the users REALLY don’t like, they can migrate to another instance way more easily than switching platforms.
Reddit is counting on the effort of switching platforms being too high for lemmy to gain traction. They are wrong.
The developers do it for free, which is common in the open source community. There will always be volunteers to build the software and donors to support them.