I suppose it's more the frustration with Southgate and his contradictions.
Lewis made his debut in England's last competitive fixture. He was played out of position and was awarded Man of the Match. He's a versatile player who can cover several positions, he's comfortable in possession and plays for the best club side in world football, under the best manager in world football—the type of player who would be very valuable during a summer tournament.
Given that, it is odd he wasn't originally called up to the squad.
If the reason is his lack of game time, then that would be at odds with previous player selections made by Southgate.
I've got no issue with Mainoo being called up either, he's a talented player and offers more than Henderson.
I just cannot work out what Southgate's plan is, other than it being the same one he has always had, which is that he doesn't have one.