Variants of that phrase is expressed by the MC when cumming in so many adult games. Why?
The expression clearly implies that the character was trying to hold it in, that is, keep the orgasm from happening. Although it's not uncommon to want to have the sex last for a while and not cum as quick as you can, when you actually orgasm the focus of making it last is long gone.
It's such a beta or submissive focus to have in that moment and to say it is just one step from actually apologizing. "I'm terribly sorry, dear, but I can't hold it anymore! I tried not to cum, I really did! SORRY!" This is obviously hyperbole, but the sentiment isn't that different.
These characters aren't written as submissive either in which case it would be suitable.
Maybe all the writers suffer from premature ejaculation? Nah, just kidding. Rather it seems this phrase has risen to some sort of standard which writers just automatically use without really thinking about it.
There are many variants of this phrase but they all have in common that negative, passive, submissive energy.
The moment of cumming is really a moment of triumph, and what the character says should reflect that. (Of course, it easily steps into cringe territory if overdoing it though so perhaps not have them celebrate like cowboys every time.)
Thoughts?