Because we don't want bitcoin to go mainstream until everyone's grandmothers can easily store their bitcoins.... the current solutions are either unsafe or way too nerdy for mass-adoption.
What do you mean?
Multibit is secure and easy to use, and there are lots of other clients that are also easy to use.
Sorry, but no. As a geek and Bitcoin-savvy user, I like MultiBit a lot, but it's most definitely not ready for mass consumers yet.
If you doubt it, try and get your mother or grandmother to give MultiBit a try. Don't explain things or do everything for her, just let her find out herself. Unless of you have a nerdy (grand)mother (which is cool) she most likely won't figure it out.
The only two wallets I currently consider somewhat "mass audience proof" are Mycelium (Android) and Breadwallet (iOS).