Wood wants to make sure his fit and injury free heading into his pre season.
Potentially going injured could see him jepordise a regular role in the team and in the prem league next year. Understandable that he wants to concentrate on this first and foremost.
I don't think motivation to play for his country is a problem otherwise he would have opted out of the Japan game like Smith did.
Another factor is this game was announced at fairly short notice on April 8 when players like Wood, Smith and Reid had probably already finalized their holiday plans. They have partners and family and friends spread around the world they would want to spend time with. They only have a month off (last season Leicester players had to return in the last week of June for tests). For example, I'd imagine Reid will be visiting his mum and step-dad in Denmark and his dad in NZ. Players don't get a break at Xmas, Easter or other regular holiday times like the general population. I can well understand them not wanting to spend a week travelling, training and playing in an international in late May.
Funnily enough Chris Wood was singled out by the Leicester Mercury to give an insight into how players find the off-season and the pre-season training last year:
[Wood said] the key was to rest and recover after last season's exploits.
Wood said he had returned raring to go, and added: "It's been a good month off to rest and recover mentally more than anything, and we've all come back in good physical shape, and it's good to see all the lads.
"We spend every day with each other for 11 months, so a month away from everything can be much-needed at the end of it."