Why do you think that many players who are lauded as the best players in the world can not perform for their national teams in the same way?

I think it's due to the fact that when they are in their prospective teams the spotlight is more on them as other players don't perform to that standard, but in their national teams they are just one of many chosen top class players who perform better.

Probably due to the England problem; choosing players over the system.

One of the reasons could be that when they play for their clubs they're so used to specific players being around them.
When they play in the World Cup they may not be as used to the people they're playing with as much as they are with their club team-mates. As the training with them will be infrequent compared to the week in week out training at their club.

Would that not be the same for every county taking part?, so don't see that as the reason.

I didn't say THE reason, I said one of the reasons.

I don't know what it's like with the training schedules of other countries' clubs.

I agree. Some top players seem very sensitive about who they play with whereas others can just get on with it.

This is why the several posts there have been on other threads, about English players declining to go play abroad for other clubs instead of languishing on the bench in England, are striking me as possibly having a lot of merit. Perhaps going to play for a foreign club helps with adaptability and flexibility.

Enner Valencia, now there's a player who has performed.

Queue for his signature must be getting pretty long.

Yes I think adaptability may certainly be a factor if our best players appear to look more impressive for their clubs than they do for England in the World Cup.