why koreans speak japanese to Japanese?

Yesterday I went to Zion Market ( korean market) next to Mercedes Benz dealer in convoy street next to Mercedes Benz dealer in Koreatown.

There was older japanese couple in front of me. the cashier who was korean american started to speak Japanese while trying to collect money.
his japanese was not fluent so he ended up speak English at the end.

Don't get me wrong. I don't hate japanese people. but why do some koreans insist speaking japanese when we can speak English.

Do Most Japanese people try to learn korean? i don't think so.
I was going to ask that cashier why he had to speak japanese.

We need to start thinking that Japanese are not superior than koreans.

they might make the Best TV or Cars in the world but that does not make them superior than Koreans.

If you have any comments agreeing with me or against my posting, Keep it to yourself.

We have second generations korean-americans who don't speak korean native language but we have people who want to speak another foreign language. where is the sense in that?