I have a couple of regular visitors to my house who just don't use the bath or shower when they come, however long it's for. I know that both of them at home bathe on a daily basis and regard it as almost a bit of a treat at the end of the day, but they don't use my bath.
I should add that the bath is brand new and clean as a whistle - guest bathroom as well so no excuse that we are hogging it or anything. And I provide them with a fluffy towel as well and nice toiletries.
It's up to them of course but TBH I feel really insulted that they don't seem to want to use my bathroom and don't get why... Is it actually normal to visit someone's house and not have a proper wash, and I've never realised?!