Why LBS only carry certain brands?

I am not new to the bicycling scene, but I am new to LBS.

I am looking to buy a hybrid bike. I'm wondering why is it that
certain LBS only carry like 1 or 2 brands and why?

My options seem to be limited to Trek, Giant (people but not stores
seem to love this one), Jamis, Scott, & Bianchi (expensive). I don't
know if Specialized makes a hybrid, but none of the stores in my area
support that brand.