it's the other way round, the military maintains the world order, the currency is used as reserve, and they get to provide services that nobody else can provide while they're top dog. they are not on a trajectory to remain top dog for very long.
Trust was its own reason. It's useful for the whole world to have a currency and business environment that operates by rules, even when the rules aren't perfect or fair.
That environment isn't being outcompeted by better, more fair rules - it's just getting vandalized for a few people's gain, and creating risk for everyone else .
But things can change no? Like the country whose currency we use becoming untrustworthy. Do you think the world watched the first trump presidency and thought to do nothing?
It was US policy to actively work against that and it was an acceptable deal for us given that we've been friends and allies forever. Now Trump has turned the US into our heroin-addict sibling we can no longer rely on them.