I think the key word is selfish.
DMs have a level justified selfishness in the DM to Player relationship. The DM do more work. There are more players than DMs. Therefore DMs get to demand more.
So if the DM wants to include or exclude elements to the campaign that have nothing to do with the theme, genre, tone, or playstyle of campaign, they can. D&D accepts a level of this due to the DM workload. Players accept this to keep DMs happy.
It all comes down to the level. Players are fine with a DM chosing the themes, tones, genres, and playstyles they like. They are okay with DMs adding or subtracting rules, fluff, races and classes based on their preferences. DMs can look for players that match their desires with higher percentages than others.
But the definition of selfishness is:
- concerned excessively or exclusively with oneself : seeking or concentrating on one's own advantage, pleasure, or well-being without regard for others
- arising from concern with one's own welfare or advantage in disregard of others
If a DM only gives a hoot about their desires, that's being selfish. Some is allowed.
Some is expected. However if a DM makes a lot of selfish decisions in their campaign, it can be looked down upon by others.