> what are the problems with showing the place around?

You and others coming during an event or even focus hours.

Also, I imagine that their willingness to do a tour at random directly correlates with vacancy rate.

It could also be a form of decorum and filtering you out. If they're not hurting for business, they'd probably much prefer clients that responsibly schedule uses of limited resources.

I've never been to a coworking space that wasn't willing to give me a tour when I dropped by.

Maybe wework doesn't like making money.

All coworking spaces I have been to have wanted me to make an appointment, and one did not even let me into the office (which was ridiculous). Maybe this is something which varies by country. And personally I prefer appointments because it makes my life easier to know for sure that they will have someone there who has the time to talk to me.