>in sexual intercourse, a lot of people seem to have decided safewords to ensure that nobody is made uncomfortable, which is great! but i don’t understand why the word “stop” couldn’t be used. why would you need to decide on a completely unrelated word for when you’d like to stop instead of just saying stop?

Because since whatever you and your partner(s) of choice end up doing might just happen to involve roleplay. If, for example, the point of the whole enterprise is to involve a party feigning reluctance, then "stop" literally and genuinely meaning "Stop what you're doing!" would sabotage the arrangement.