They go for cities where they feel like they have a chance, and where there are not already 10 other competitors. That's why they didn't go for e.g. London.

At least that was the original thinking of one of the founders, according to an article I read in some in-flight magazine.

That was indeed the original strategy. It's changing as the company grows though.

Food apps are extremely popular in central/eastern eu, here in Czechia the local DameJidlo is also a largely successful company. Wolt is now becoming a serious competitor to them, they already have a much better app.

Not to detract from your point re competition, but isn't DameJidlo one of the brands of Delivery Hero? Do they have an engineering office in Czechia?

It was sold to DeliveryHero (if that's indeed the current owner), originally a Czech company; they had a rather large engineering centre here when it was still Czech, not sure about the present. The founder went on to create Rohlik.cz

Probably a good data point that some of these delivery services are relatively local.

Something like Uber there's an advantage for travelers to have it in a bunch of different places if they already have the app installed. On the other hand, I don't even use Uber once a year locally.

Whereas with food delivery, I don't really have decent options. But, if I did, I would probably use it now and then at home. But I think it's accurate to say that I have never used food delivery while traveling.

They're also present in Central Europe but they're in no way the most popular.