Buying a bicycle - your options or the lack thereof

It just happened so that I was near a bicycle store recently and decided to peek in purely for entertainment reasons. I'm not interested in buying a new bike at the moment, but the store in question advertised on its front that Trek, Specialized, Surly and Salsa bikes were sold there. I figured it would be good to see if the newest 2017 offerings by Surly and Salsa already arrived and check them out in real life.

Unfortunately, that wasn't the case. In fact, after carefully checking the on-the-floor inventory, it turned out that not a single bicycle showcased was different than either Trek or Specialized. That made me think that I have seen similar situation in many other stores previously. The Two Big Guys (Trek and Specialized) sell their products in essentially every single bike store around. However, if you wish to purchase a bicycle from a bit lesser-known brand, such as Surly, Salsa or let's say, Kona, you're out of luck.

 

Specialized Roubaix - sold in every single bike store near you...

  

... but if you prefer Salsa Colossal instead, good luck finding one.

Why is that the case?

Could it be that Two Big Guys have such a strong marketing power (Or is something else?) that they require bike shop owners to present their products (nearly) exclusively?

Could it be that other brands are not showcased that often, because "they don't sell well"? But then I could argue that they would sell better if they were actually available in store.

Could it be that those niche brands offer bicycles that are too expensive for an average mortal? Unlikely. You can have a Salsa bike for not more than $1000. That's well in the same ballpark as majority of bikes from the Two Big Guys.

So what is it? Why a store that advertises to sell other brands doesn't have a single bike available for a test ride? When asked, owner's response is usually - "We can order it for you", but that's not the point! I can order it online myself, but I would be much, much happier to try it out at a local bike store, buy it there and likely spend even more money on some extras too.

I would think that a bike store offering those "different" brands could have a marketing advantage. After all, why should I buy this particular Trek bike in "my" store if 5 other stores nearby offer it too?

If you are a bike store owner, please help me understand this.