It's a modelling tool. Pretty sure there are plenty of users (e.g. artists) who don't care at all about source availability. And, this is why I say the license

It's a modelling tool. Pretty sure there are plenty of users (e.g. artists) who don't care at all about source availability. And, this is why I say the license is lenient: most freeware creative tools will also try to lay their hands on what you make using them. (e.g., edu versions of modelling/CAD software will also impose restrictions on the files you make using them, meanwhile this doesn't even require attribution let alone restrictions on commercial use of the output)