One thing that I do not see mentioned is the likelihood of encountering surprising triggers in a given game, and how this might affect how people see ways to avoid them.

Some games contain body horror, or emotional violence, for example. Others do it far less. For many games, it is hard to say.

Some games try to cause specific strong emotional experiences. Many do not.

In some games, there are many participants who can introduce whatever content to the game. In others, you running a tight script with little chance for anyone to deviate.

In a convention with games like Road to Vasen or Monsterhearts, having some explicit safety measures is an excellent idea. They try to create emotionally intensive and heavy experiences, and you might not know what you are getting into, especially with various Fastaval scenarios.

OSR body horror games are usually easy to spot, and they typically do not try to go deep into emotional issues, so it is easier to trust the judgement of the players to self-select into games that are appropriate for them.

Then there is stuff like organized play, non-body horror OSR dungeon crawls, and plenty of other games that very rarely go anywhere near emotionally deep issues.

Then there are, of course, various games with plenty of shared story creation, where nobody really has any idea what is going to happen.

There are also competitive games, or games where one is fighting as a team against the scenario, and in these one expects strong feelings due to losing or winning and other such concerns. (This is a different issue from the one discussed above, where people would use an X-card to lose or to win, which I doubt would be a common problem.)
These feelings can be very pleasant or unpleasant, but using the X-card would be a completely inappropriate response. Having it available obviously does not force anyone to use it, but one would have to be somewhat nuanced about explaining when it should and should not be used.

There is also the case of someone springing a surprise rape scene in the middle of you Dungeon world game, or whatever. X-card has no power to stop an intentionally malicious person, though it can make their behaviour easier to spot, maybe. Or maybe they would use it as a means of attacking someone. Anyway, I doubt any safety measure besides personal intervention or walking away really helps here.

In all of these contexts, the need for explicit safety mechanisms is quite different. Claiming that everyone, everywhere, should use or not use a particular tool is quite a strong claim.