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?
Happens in germany too. A lot of people get a special salary at the end of the year, Christmas money if you will, and that also accounts into the yearly salary. If I earn 4K a month, I earn 48K a year, but if I get 100% christmas money, I earn 52K.