Barely used doesn’t mean useless

They’re not for regular people making regular transactions, it’s kinda intended for high value transactions

Wealthy people selling things (semi-)privately to each other is one obvious one, things like those £50k watches. Sometimes these wealthy people want to do their spending with utmost discretion, so cash is king.

Another is pawnbrokers, private currency exchanges and similar kinds of business that just have to deal with a lot more cash than is typical.

Don’t get me wrong, its usage will definitely be in decline, but I don’t see them taking it out of rotation any sooner than the fiver