Cars younger than last century have two modes of indicator available.

[ BMW, Merc and Audi drivers: nothing to see here. Not in this whole post and comments. ]

A soft push in either direction gives a brief - I don’t know what the definition/legal requirement is - period where the indicator flashes before cancelling itself.

A harder push has the indicator stay in that position until the steering wheel or the driver cancels it and it stops.

Maybe you’re complaining about people using the soft mode.

In my country, there is no requirement to indicate when moving back to your lane after moving into the/a overtaking lane. I think that’s a little weird tbh. I’ve always indicated, wherever I’m going, on the basis that when I don’t, someone will sideswipe me through my own negligence.

Of course, these days the sodding lane-change Nazi in my car won’t let me pass any line, but happily forcefully steers me into the hedgerow/ditches on country lanes where there are no road markings. You can turn it off every time but not generally.