It's been 10 years since you could first do it in e.g. Stockholm with normal licensed taxis.
Edit what I mean are regular taxis, not "black cabs", "minicabs" etc. I mean the iconic taxis. If you can't hail those, why not?
In any case: being able to hail a taxi on the street doesn’t mean it can’t be useful to pre book one with an app too. I you want to go to the airport in the morning from a house where few taxis pass, that’s what you need to do. In the 90s that meant calling a phone number but these days you want to use an app, pre pay in the app and so on.
(On a side note, I take buses every day but I have never seen someone signal for one. If I’m at the bus stop it stops, if I’m not - it doesn’t. This varies between cities too I guess)
'Black cab' specifically refers to the famous London cars that have a particular shape.
I agree. Black cabs are hailed though, that's the point. You don't call a black cab, that's not how they work. That's what private hire (e.g. Uber) is for.
WRT buses: almost everywhere in the UK is request stop, or at least I wouldn't rely on just expecting the driver to guess.
There might be ten different buses stopping at your stop for example, so it's inefficient to just stop anyway, unless someone is already getting off.
You should think of black cabs as vehicles for the wealthy to potter around Central London avoiding public transport, or for tourists to get mugged.
The average Londoner doesn't really use them.