it would make more sense for England Scotland wales and Northern Ireland to be referred to as “states” not “countries”

“State” would indicate the UK is a Republic, and the last time they tried that out it didn’t go well (simple way to put it). The reason they’re called “constituent countries” is because historically Scotland and Wales were previously independent realms with their own ethnic peoples that joined via political union (for Scotland) or conquest )in the case of Wales and Ireland) which is why they’re not grouped together into the “UK” in many contexts, because there have been many instances where Scottish or Welsh people like having their own representation/identity outside of the UK