For me it's not the online-only or closed nature of the thing, so much as the fact the canvas isn't high-DPI, which I find unreasonably maddening (I am unreasonably snobbish in this regard).

And the grid-oriented working method isn't ideal for me, though I confess I've not gone back to look at TinkerCAD much since learning OpenSCAD and FreeCAD; it may be that a better-informed visit would show me where I was judging it too hardly.

But it is amazing what people do with it, and while I have my issues with AutoCAD, it's clear that TinkerCAD is a truly liberating tool for an enormous number of people, and my criticisms may be getting into gift-horse-examination territory.