The market must be pretty small for Mac native text editors (and they must be difficult to implement on a grand scale). Otherwise some company would have walked into the gaping void that has been the delay to release TextMate 2.0 and released something by now. The door has been wide open for some time but no one is able or willing to step through it. Oh well, helps explain the Vim goldrush of the past few months.
Also, the market is probably not large enough. Paid market. There are lots of free editors, and commercial editors, already available, and there's a skill learning curve required to switch editors, that I think all of this adds up to explaining the unexploited "gap" you described.