Copa takes place during a similar timeframe and you rarely see NTs take it with so little seriousness. AFCON is held in the middle of the European club schedule and still get strong sides. Even the Asian Cup is taken seriously. I think it’s weird that big sides have decided to prioritize the nations league over the federation cup.
Could be the fact that the Gold Cup is the most transparent money grab there is in the whole soccer world, always held in the same country. Always drawn to maximize the probability of USA v Mexico selling out a big stadium for the final. With the excuse that it helps pay for everything else in the confederation.
Prioritizing Nations League seems like a load management thing. 2 games instead of 6.