Most non-technical users aren't going to remain interested long enough to try even a few desktop environments. The first one they use will leave a strong impression.

I would argue that having a choice between hundreds of DE's is a bad thing for the more casual user.

Please stop this. "Casual user", "average user", "normal user", it's all just so much bullshit people tell themselves to feel superior. Stop creating this strawman and using it as an excuse for why things have to keep sucking!

ChromeOS and Android adoption prove otherwise.

The large majority of their users don't even know what kernel is running the runtimes of their apps.

One of the reasons of netbooks failure, besides the cheap Windows XP licenses move from MS, was that each netbook Linux was its own little silo.