Well, relevance is a thing: if you're a site that focuses on a geographical area (local site for local people), you don't need or want people from thousands of miles away coming; it's just not relevant. Anything that has a geographical component for relevance is likely to be considering restricting access to far away places.
Then of course you have the fact that China, Russia etc. bots don't necessarily respect crawl delays or robots.txt files and they're just chewing up resources for little or no benefit - if you don't see people from these countries coming (doubly so if not relevant), might as well block at the door and preserve your resources for actual users who will get some actual benefit from your site.