This is more an inference than a citation but ESRB reports react
extremely badly to anything sexual, and double and triple down on anything that isn't extremely vanilla.
Mass Effect 2 has a legendary example, and
Dragon Age Inquisition an equally infamous one. Notably, roughly half of the summary is devoted to discussing sex, and one quoted line (the "I will bring myself great sexual pleasure later" one) is not actually spoken in any real language during the game itself (it's atmospheric dialogue the Bull may mutter in Qunari language while fighting one of the area boss Dragons, which is not even subtitled by default). Similarly, the ME2 entry is focused more on dialogue than actual sexual interaction (and it cherrypicks the line about Krogan sexual deviants, demonstrating that this was a concern for them).
I know this trend has been observed in American fiction going back to at least the 70s:
"You can show a dozen guys on TV murdering each other with knives, but you can't show two people making love." is a line from one of Spider Robinson's
Callahan's Cross-Time Saloon shorts, and it remains as true today as it was then (at least, for regular TV, rather than PPV or streaming services).
To give another example, the existence of the leftover data for "Hot Coffee" in San Andreas resulted in it receiving an ESRB R rating and being pulled from shelves at stores around the world (in fact it stayed off the shelves here even after the rating was downgraded for the rerelease for a bit). In the same period, Manhunt - a stealth game that sold itself on brutal stealth executions and gory attacks - went to shelves with only an M rating, due to a complete lack of sexual situations or even dialogue in the game. (... that I'm aware of, I haven't played it basically since it came out.)
As near as I can tell, this prevailing thought with the ESRB hasn't changed: murder and gore ok, sex - even
talking about sex (even talking about masturbation!) - very very bad, and god forbid you try and do something actually kinky.
I have some theories about what's going on with that based on recent sweeping changes in reputable literotica publishing houses but that's even less of a case of "I have come to this conclusion based on looking at games for 30 years" and more a case of "I'm pretty sure this is the case based on suffering through using twitter a few times a week" so I wouldn't really care to discuss it as if it had any weight behind it.