A lot of people are buying stuff with bitcoin (as I am). Bitcoin is probably being used more than you think
But why people will start using any altcoins if they can already use bitcoin for the same purposes?
Not that I think Bitcoin will get thrown of the throne soon, I can't see any alt coin doing that at the moment (but never say never). But I wont say, there won't come an altcoin in the future that will.
Imagine an altcoin with the same features as Bitcoin, but with instant transactions and no need to waist electricity on mining them (or uses the electricity for something really useful). Still sure people would prefer Bitcoin?
Yes, because everybody else will be using BTC and you will be only one of a few using the new alt.