They briefly touched on, "can't imagine spending that much time on a trainer", but I think there is a physiological reason why a protour rider cannot get in shape on a trainer, whereas you and I can.
The problem is their massive FTP and watts per kilo.
For every watt that goes mechanically to the trainer from our legs, there are roughly 4 watts of heat generated. So this is how the match goes.
Let's say Nairo's Quintana is riding at say 70% FTP. If his FTP is around 6W per kilo (I don't know exactly what it is, but close enough), then 70% is 4.2Watts per kilo.
Now let's translate that. He ONLY weighs around 58 kilos, so when he is cruising, he is riding at 240W. Which means he is generating 960watts of heat.
This is Nairo basically doing no work. If he does any quality, and ratchets it up to 5W per kilo, he is generating another 250W per heat so now he's hovering at 1200W of heat...if he goes at FTP he's getting close to 1500W of heat.
This is a tiny guy like Quintana. Once we get to the 70kilo riders, at 100% FTP they are generating 1700W of heat.
So basically a protour level rider can never get tot he intensity levels as outdoors while indoors because there is not enough cooling. So until they can get outdoors they just can't do enough intensity without overheating. Thus all the guys stuck on trainers, came out of lockdown out of race shape. They can get in shape just not race shape like the Slovenians who could train as much as they wanted outdoors (same with Colombians).
I think Rappstar alluded to this a while ago that age groupers could get in shape for the level of performance we have to, but pros training exclusively indoors can never get to their real high end. Maybe for Ironman level pros its not the end of the world but for protour riders (or even ITU), there is more fitness to be had outdoor training.