I haven't had Wifi in any of my flights between Thailand and Amsterdam (KLM). Maybe I've always had older planes on this route or something. I haven't flown between any other 2 destinations for the last couple of years.

It really depends on the airline, but it's fairly common to put newer aircraft with WiFi on more business-heavy routes, and put the older aircraft on more tourist-heavy routes where passengers are more cost conscious and probably won't pay for the WiFi or other amenities either.

Yes it's because there's no pan-european ground network yet so airlines are limited to expensive and slow satellite internet.

However this is coming soon: https://en.wikipedia.org/wiki/European_Aviation_Network

I think it’s starting to become a thing, but even in the US the last time I tried it just wasn’t working.

Also worth noting that cell phones work normally on trains, what with them being on the ground, so you're not even at the mercy of the operator - you can just use your normal service.