[All] Why does the smartphone keyboard make a sound effect when I press it?

I'm going on a trip by KTX this time.

Among the KTX passengers, there was a man in his mid-40s.

He kept saying "tap tap tap tap, tap tap tap tap" and was using something like KakaoTalk while keeping the smartphone keyboard sound effects on...

I don't know if it would be good if the sound effects were good

It was a really annoying sound, like typing on a mechanical vending machine.

I thought this was a feature only used by middle school students and younger haha

I was afraid it would ruin the mood of the trip, so I tried to ignore it and endure it.

The sound effects were louder than I thought, so I kept getting nervousㅠㅠ

I'm really curious, but in a public place

Why do you guys use smartphone keyboard sound effects when you send KakaoTalk messages or search?