I have no idea.
I went to Wales for the first time ever last year with some mates - we went into a pub in North Wales, asked for a pint of carling, and the guy behind the bar COMPLETELY ignored all of us...
Then about 6 Welsh guys who were talking English when we walked in, all started to talk Welsh and they were laughing at us, etc.
Then the bar man turned around and asked us to take our hats off (baseball caps) before he served us, which made the other Welsh guys laugh even more.
It was horrible and I absolutely hated it. I had nothing against the Welsh before this happened, but it is nation-wide in Wales because a similar incident has happened since then in the South!
Needless to say I will not be going back there again.
Here in South East England, my local pub always welcome tourists, especially Scots and Welsh, etc to our village and we make sure they have an excellent time, by getting them absolutely legless!
We have a great laugh, I just wish I could say the same when I go over to Wales!
I don't know why they hate England so much, they never seem to be able to give a proper logical reason - I suspect possibly jelously?