Worldbuilding and believability are much more important to me than making sure every possible heritage and class is available and every combination is represented. Players can almost always find something they like in the available options.
So you put a small increase of your enjoyment over a potential huge decrease of enjoyment of others "almost always".
Also there is a huge difference in "find something enjoy playing" and "play whst you enjoy most".
Also 1000s of games and 10 000s of GMs manage to make believable worlds where all combinations are possible, so its not like this goes against believability per se. Its just that you personally dont manage to create a believable world where this is possible.

