Why the sudden popularity of .io domains?
- They're available…
- …probably because they're significantly more expensive(from any registrar I've ever seen) than the usual TLDs…
- …and somewhat desirable to techs because of a cheap I/O joke.
The usage itself among web/tech people isn't terribly new. There were several bloggers who started using the TLD years ago that I can't remember at the moment. Over time, it just seems to have slowly built an association with those sorts of people and their output/products. You have to remember that it's gotten really hard to find a decent short domain with .com et al, and very few alternative TLDs like .ws have ever gained much traction, so there's a bit of community convergence going on here, stemming in part from that shared joke.
I guess it's just because most people would not relate .io TLDs to British Indian Ocan Territories, but with input/output or whatever abbreviation seems reasonable for the specific domain.
The same thing is happening with .tv TLDs, which is for the island of Tuvalu normally, but is more commonly interpreted by people as an abbreviation for "television".