I think this is mostly a US thing. Why use yearly salary? You’re not paid once a year, are you? Most likely once a month. Referencing monthly salary makes much more sense.
“I’m making 50k”. Great, now I have to guess - dollars? Monthly? Yearly? If yearly then what’s the monthly paycheck? Net? Gross?
Generally the people you’re telling your salary are people in the same location as you or at least the same state.
Telling the yearly salary makes the most sense there since it should be similar weekly/monthly amounts. And even if they aren’t in the same place and it doesn’t translate based on tax differences, telling someone the monthly or weekly payment would make no sense.