I don't know much about Blender, but the other two, at least, have had substantial contributions by paid engineers (at big, well-known corporations), and likely

I don't know much about Blender, but the other two, at least, have had substantial contributions by paid engineers (at big, well-known corporations), and likely input from non-engineers (e.g. product staff). They're exceptions to the rule of (F)OSS.