1) A lot of DX stations seem to prefer below 1KHz. Also Fox/Hound mode (also usually DX) requires them to stay below 1KHz. So some people try and keep that free for the DX stations.
2) As mentioned a lot of radios don't work well close to the band edges. If you stay away from the edges you don't have to worry about that. Your radio may work close to the edge but by doing so you are cutting out a lot of contacts from people who's radio doesn't work well there.
3) If you are trying to work a DX station it helps to lower the base frequency by 300-500Hz. This now means that the top end of the FT8 band is no longer available.
All of these combine to make it more likely that there will be fewer stations on the high and low ends.
Nothing wrong with your choice and I can see where it will help you make contacts by lowering the competition. I can't imagine any rational person complaining about a QRP station operating there. 1500 Watts? That's a little different. Of course this is ham radio. An assumption of rationality may be a bit naive.