In some “ecosystems” everything being free is kinda how you are compensated, instead of money. You spend time making your thing for free, but so does everyone else so you don’t have to pay for those things either. The two main examples I’ve personally been involved with are game modding and 3d printing models, I use the free stuff other people make all the time, releasing the things I make for free is how I pay it back.

But yeah, if you use something you really like, throw them a buck or two for the work.
…although I’ve donated about as much as I’ve received as donations myself. Eh. No matter.