Bikes on Eurostar?

Why does it have to be about profit? Why not be clever and facilitate active travel and reduce need for cars? When the planet is underwater, your profits, as well as your Strava KOMs are gonna be fucked.

That Eurostar carries bikes at all is an anomaly in any case. From memory, but I can't find anything about it on-line, cycle carriage was only inserted into the legislation because of a Tory MP's (or maybe Lord's) intervention. I think the only other high-speed train, possibly worldwide (but I'm no expert on trains, so please correct me if that's wrong) to allow bikes on is the German ICE 4:

https://ecf.com/news-and-events/news/deutsche-bahn%E2%80%99s-new-ice-4-high-speed-trains-include-bicycle-spaces

When European high-speed trains first started in France in the late 70s, cycling was pretty much the 'forgotten mode', and at any rate the main strategy behind European high-speed trains has always been to facilitate business travel, e.g. the famous 'it's competitive with short-haul flights'. In France, this has led to a two-tier rail system, with very little investment into local and regional trains, in marked contrast to the TGV network. In Germany, this two-tier aspect was made very visible by last year's €9 ticket, which allowed unlimited use of local and regional trains, but not ICs or ICEs, for a month. This is now being made permanent, albeit with a higher price of €49.

tl;dr--high-speed trains were never introduced for the good of the planet but 'for the economy'. What have cyclists ever done for the economy?

Imagine if they made it a genuinely useful service and priced flights appropriately, how many flights could they cut?

Well, I don't think any meaningful action is going to be taken on flying in our lifetimes, I'm afraid. Anything that would make things better would involve 'less', which is a forbidden word.