Why dont people use scout bikes???

I think scout bikes are pretty sweet, they get grenade launchers and can set up traps in terrian. They pretty much have the same wargear as a regular space marine just a 4+ save instead of the 3+ but overall the fact that they can scout, and infiltrate seems pretty good to me, plus the above mentioned bonus seems pretty good.

So why have I never seen anyone use them before???

* They are Scouts, but
* They cost +7 points more than a Scout
* They lose "Move Through Cover"
* Unlike a Scout, they cannot mechanize

Combine all above with:

* Models are relatively new and rather pricey

Yeah but why not use them instead of normal bikes?

better question: Why use normal bikes outside of one specific army build?