-
A rider's season is carefully planned, especially a leaders like Pogacar. His training is tailored to meet his objectives for the season, so at the start of the year the team would've planned that he'd be in good form for his first racing block in March (Strade Bianche, Milan-San Remo and the Volta a Catalunya), eased back on his April training a little so he was race fit and fresh for Liege-Bastogne-Liege, then carefully built his form for the Giro and the Tour. Between the two races he was at altitude in Isola 2000, so he's spent a lot of time away from home training and racing.
His plan for the rest of the season was to extend this racing block by a fortnight to do the Olympics (which he's now withdrawn from) then probably have a holiday before training for the Worlds and Lombardy (his end of season goals). That's a lot of peaks for a rider, even one as talented as Pogacar, and it requires a solid base (which he'll have worked on through most of the winter and early spring).
He probably only has a break at the end of the season of a few weeks, definitely no more than a month, which means his body is always being stressed by training and racing. There is a chance he could do the Vuelta and win, but what is more likely, given that he's not planned to do it, is that his form will just fall of a cliff as his body struggles with the additional load of an unplanned race.
It is possible to ride three GTs in a season, and plenty of riders have, but no one has ever come close to winning all three in one year. Chris Froome won all three consecutively (the Tour and Vuelta in 2017 and the Giro in 2018) then did the Tour, where he finished third, and he has talked about how much he struggled after that as the load over a 12 month period was so high.
He has an opportunity to be the greatest rider of all time. To achieve that he has to race consistently for the next five seasons and win more of the major races. Compromising that to satisfy internet forum people’s desire to see someone attempt to win all three GTs in a year is pointless.
I want to see a contest between a fully fit Pogacar and a fully fit Vingegaard at the Tour next season. I don’t want a repeat of the past two Tours where one of them has arrived at the start line having had their preparation compromised by injuries caused by crashes.
Riding a third GT this year will definitely compromise Pogacar’s preparation for next year.