I see this on job/ career/ interview subs all the time, they say it is extremely important and bad manners not to. These are predominantly USA citizens.
I’ve never written a thank you. I think they should be thanking me, for taking the time and effort to apply to work for them. I’ve had great success getting jobs when needed, so it hasn’t hindered me. I will say thank you in person if it fits in naturally, but I say that to everyone I meet in a business capacity.
So, is it part of your countries job application culture to send a thank you email to interviewers? Also Americans feel free to point out if this is not actually expected across the board.