meaning in context - Why does he go "pink with the effort" while watching morris dancing?

This is a follow-up question to my previous one, WHY did he go slightly “pink” ?? Does it mean angry, embarrassed, healthy or other meaning in this sentence?, as in that one I have established that "pink" in this context mean "embarrassed" other than "angry or healthy."

Then it leads to my second confusion, why is he embarrassed? I have checked the definition of morris dance on wikipedia, so far as I know it's a culture dancing, some cultural heritage. but why embarrassing? is there some culture gap I have missed??

Here is the sentence:

We, in the meantime, had gradually been increasing Will’s outings—and the distance that he was prepared to travel. We had been to the theatre, down the road to see the morris dancers (Will kept a straight face at their bells and hankies, but he had gone slightly pink with the effort), driven one evening to an open-air concert at a nearby stately home (more his thing than mine), and once to the multiplex where, due to inadequate research on my part, we ended up watching a film about a girl with a terminal illness.

Me Before You by Jojo Moyes

I searched the whole novel, and there are only two times "morris" are mentioned, the other is in a conversation in a horse racing watching:

‘Don’t be grumpy. They say you should try everything once,’ I said.

‘I think horse racing falls into the “except incest and morris dancing” category.’

‘You’re the one always telling me to widen my horizons. You’re loving it,’ I said. ‘And don’t pretend otherwise.’

Me Before You by Jojo Moyes

The context is that Will is a quadriplegic in wheelchair and he rarely goes out, and he does not like go watching horse racing. "We" means Louisa, his carer.

Could anyone help with this question?

Answer

To augment Jeff's answer...

"To keep a straight face" means to refrain from laughing or grinning; to succeed in an effort not to laugh despite the urge to do so.

Morris dancing dates back to well before Shakespeare's day. It is not a mainstream tradition that nearly everyone enthusiastically engages in; rather it is a form of folk dance being kept alive by local troops and by clubs on university campuses. The practice is regarded by many as hopelessly quaint and silly.