Display space in any retail store is precious. It's finite and valuable real estate in the store. You display what's most likely to sell.
On the distribution end, many retailers don't even select what magazines they get. (I had a temp job once at a magazine distributor and this is what I was told so YMMV) Instead the distributor keeps track of what sells and doesn't and stocks accordingly. Personally I despise CVS for other reasons, so by all means don't shop there.