large part of Europe also.
also yearly before tax, because employers do not need to know about other incomes and thereof how much money you pay in taxes. you can tell, but they don't need to know.
when they hire you, they don't know about your taxes, anyway. they put the ad, and if you're hired and have other incomes, you'll pay more taxes out of it.
yearly because taxes are paid yearly.
some people are paid weekly, some monthly.
so yearly becomes the comparison to help taxes and compare across the market which might pay at different frequency.
it helps account for your budget and their budget.
if you don't care about budgeting or calculate taxes, you make the math.