Of course, the point about their license is a good one, which definitely has some limitations on what you can do with it: https://github.com/harness/drone/blob/master/LICENSE (I wish I earnt 5 million $ and this would be a problem I'd have to think about).
Thanks for bringing up Woodpecker, though, it also seems like a nice project and the two CI solutions haven't diverged far enough for migrating over from one to another to be too problematic, should that become relevant in the future: https://github.com/woodpecker-ci/woodpecker
Of course, as I said, some folks might also prefer something like Jenkins or another CI solution. I'm yet to explore most of the packages out there!