Since hacking on a 3D DCC in your spare time may be more than three times as enticing to people than doing the same on an email client?
I'd wager Occam's razor favors this explanation.
but still, they were open sourced about 1 year apart. I still think having a bigger user base is a good reason for the difference
It's come an absurdly long way since I first dabbled with it in the early 2000s, and has gone from a niche FOSS tool to something widely used in its field.
Nowadays, Blender is an example of masterful UX for a professional tool. Immediately responsive, information dense UI with keyboard shortcuts for absolutely everything. Actions are composable, like with vim: something like "ex5" will extrude five units on the x axis.