Yeah, this matches my experience.
System shock was typically forgotten about as long as nobody mentioned it. "Ok you can do that, but you might die instantly," isn't a particularly good mechanical design for a game.
From my experience, there were a lot of rules in AD&D which, during the campaign pitch or session 0, the DM would assure everyone would be religiously observed. Alignment penalties. Elf raise dead restrictions. Demihuman level limits. System shock. Death due to aging. Training costs.
However, once it came time during the game to actually enforce that rule, it would often get waived because it wasn't fun. "You can't level up," or, "you can't come back from the dead," or, "you're too old," are just outcomes to the game that aren't fun. If the object of a TTRPG is to keep the game going, then rules that make the game stop are contradictory. Sure, you could roll a new character, but it seems like a lot of extra effort to do that when nobody at the table wants to spend the time to do it.