It's because it's harder to do that the normal cycles and things can end up in an algae disatster if things aren't done correctly, people don't like the addage of looking after plants also. You obviously nailed it without knowing. I also have never fishless cycled a tank, all of mine have been silent cycled. It's much easier IMO that messing with ammonia and stringent testing with kits. The best test kit a planted tank can have is the plants.