It’s worth noting that the train problems in Europe are relatively well known (some of them, anyway), e.g.:

1. Train fare from country A to country B will differ on each of the 2 official national websites involved for the very same ticket. So you might benefit from buying from the destination country (in which case of course you must do so online which nixes cash).
2. Different train scheduling websites show different inventory; you must visit both national ticket sites plus some third party sites to become aware of every possible train.
3. (Germany) The train app is closed-source & exclusively available from Google/Apple.
4. (Germany) The train site’s “necessary cookies only” option actually includes many shitty 3rd party surveillance advertisers (thus they mean necessary for business, not technologically necessary). They are being sued for this.
5. (Germany) Some tickets are only exclusively available through the app. Not all ticket inventory and prices are available at all points of sale. I heard there are some stations where in some situations you’re fucked if you don’t use the app because they are removing kiosks under the nasty assumption that everyone is a happy smartphone-owning patron loyal to Google or Apple.
6. (Belgium) The only Tor-reachable train data is the irail.be site, which does not show prices and which is missing more than half the inventory.
7. (Belgium) Weird requirements to get low pricing in some cases. E.g. there are cheap “cross-border” tickets but they can only be bought in a bordering station. So if you want to go from Antwerp or Brussels to Lille, to get the low pricing you must buy your ticket to Tournai (a border station) and then at the Tournai ticket window buy the ticket to Lille (hope the window is open when you arrive!). So you can’t even buy the tickets for all segments in advance.

That’s just a sample of problems in this train shit show. The EU Commission actually tried pushing some legislation to fix problem ① (and I think ② as well) years ago but still today there has been no progress.

So if the Commission can’t fix that mess, what’s Spain to do? Spain needs a stick because the carrot is not working.

Soon those short flights won’t exist as everyone is taking the train.

Even if they fix the train ticketing situation people don’t want the risk of making a separate purchase for the ground portion of their trip. If you miss the plane→train connection or vice versa, you’re fucked. I’m not sure if Spain has train codeshares in place to remedy that. (I forgot what those tickets are called… is it airtrain?) And note as well the codeshares still have the problem that an airline will do an exclusive deal with a train operator. E.g. train-plane itineraries involving CDG are only offered by Air France and for Amsterdam it’s KLM, AFAIK. Which is a kind of monopoly.