It seems to be a matter of timing. The "r" fad happened when some important niches were being opened. The ly and ify fads just don't seem to have coincided with anything anyone needed or wanted.

I'm sure there's some new fad waiting around the corner in both TLDs and application domains. We'll have to see if any of the apps turn out to be useful and sticks around. The TLD fad will surely explode and then disappear.