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?
In Spain it is also yearly. In general the annual salary is divided in 14 payments, unless you ask to have it divided by 12, depends on the employer, so it makes sense.
The income tax is also annual based. So depending how much you earned during the fiscal year you have a different tax rate. (And part of the income tax rate is dependent on the “state” but they are all more or less similar).