Flying is a fraction of the cost of the Eurostar or one of those long-distance trains. I'm not necessarily saying it is good (flights do pollute more), but until taxation is used to level the playing field and set the right incentives there's no reason to inconvenience oneself. Surprisingly I've also had way more luck getting last-minute plane tickets than the corresponding trains (and last-minute tickets are often still cheaper than a typical Eurostar).
Internet connectivity is still not a solved problem (transport companies are hell-bent on always outsourcing it to the most incompetent lowest bidder), so many kinds of work just can't be done on a train. I'd rather take 2 hours offline in a plane than a full day on unreliable cellular or train wifi.
Some routes now also have airport-style security theater with luggage x-ray and "take out your laptops and put it in the trays", so that's one less reason to take the train.
Legroom still stands though, but with the duration of a typical intra-EU flight I find it not too big of a deal.