This only works if your mitm ca is preinstalled in the client device.

No, because that will simply fail.

I did see it once on a train in the UK, but that's the only time I've seen https MITM.

I've never seen this. They usually just block all HTTPS connections and rely on automatic captive portal detection in modern OSes. Occasionally I've had wifi that had a captive HTTP portal but would allow HTTPS through anyway.

> airports especially

Indeed, lets not forget what the Snowden leaks said about airports:

https://www.cbc.ca/news/politics/csec-used-airport-wi-fi-to-...

I haven’t seen that in about 15 years: the experience is horrible and will get tons of complaints.