Because there are some people seriously fucked up in a head and thousands of others lacking basic decency?
There appear to be some trolls now who book tens of covers in different restaurants as a prank. Leaving them empty or partially empty. Starting different emails for each booking, doing the booking. Wth. That's some dedication to hurt already hurting businesses, isn't it.
It's bad at the best of times with people booking and not turning up (many restaurants have big issues with this across all price brackets). There was someone saying last year that their friends book two restaurants for a weekend and decide that evening which one they fancy more...
AIBU to think they should all ask for deposit? Some already do, but some seem to be worried about trying for some reason.