Why? Probably too much wax.

This, of course, is why we used to keep a tiny bottle of olive oil in. Back in the old days before we realised that some people ate the stuff. Warm a teaspoon, put a little oil on it and pour into ear. Tilt head to get rid of it. Wax reduced.

Seriously, I don't recall ever seeing a singer do this, except people taking the mickey, in fact it was from the Michael extraction that I realised it must be a 'thing'.

And I now enjoy oil and vinegar salad dressings: in the old days pure vinegar was all we used and that mainly came from the jar the pickles had been in.