This is definitely -not- true. Almost all of Best Buy's display TVs on the floor are 4K. They want to sell you 4K tvs. They cost more and they want you to buy other 4K related shit.
Might depend on the Best Buy (e.g. my local one still has an original Xbox One with Kinect as a demo station) but here they overwhelmingly have more 1080p (or less). Remember you can't get 4K for the 32" or less category of TVs, and they still have a lot of sub-tier brands, and if you go down to 20-something inches they start having sets that won't even do true 1080p. They're not on display for the most part, although their displays are mostly sets costing close to $2000 or above that.
Seriously, where have you been? At least in the US, I've been able to stream 4k for almost 3 years, not even counting UHD Blu Rays.
Their catalog hasn't expanded in that time to really include anything that isn't a Netflix original. Like right now (Canada) my 4K options which aren't Netflix-owned media are:
Terminator 2 with too much DNR
Bram Stoker's Dracula, subtitles for the opening sequence are missing
Crouching Tiger Hidden Dragon
Talladega Nights
Planet Earth II
maybe Breaking Bad? Not sure if it's still available.
Amazon Prime I don't think has anything in 4K that isn't a Prime Original.
And outside of sports I don't think you can even do 1080p with any TV provider in North America.
I suspect in a year or two we'll just be seeing a lot of setups like my in-law's, who dropped like four grand on a curved TV but exclusively watches cable TV which last time I checked was plugged in with component cables, with his DVD player (I think mostly unused) plugged in via composite cables. Also I'm pretty sure none of my parents' TV's (they own about 6 total across two properties) even do 1080p; maybe the one they got last year does?