England May dates more expensive?

I imagine it’s because it’s a particularly popular time. It’s generally a lovely time to be here.

Festivals up the wazoo all over England, some of the best weather of the year, plus the Chelsea Garden Show

And lodging seems more expensive then.

Because I guess the May tours are more popular and best-sellers?
Plus, hotel rooms go up in May, generally speaking.
The most expensive hotels of your trip will be in Bath and London (beginning and end of your trip).
These costs will be passed along to your tour company, so they price the tour accordingly, I'm sure.

May has, hopefully, warmer weather than April....but you never know.
We went on the Best of England tour beginning April 15, and it was very, very! cold by the time we arrived at Hadrian's Wall about April 25 or 26, with strong winds blowing out of the north.
If we did this tour again (with friends who have never been to England) I would go in May or June, regardless of how much more it costs--well, within reason of course.

May is the best time to see gardens in England and I think this is one the big draws for a lot of visitors.

Thank you all kindly for responding!