A lot of people saw the potential but in 2007 there still were worries. Apple whould have been crazy not to let people develop app for the device but it wasn't possible until july 2008. Also many programmers were worried on how who apple would run their store as soon as they annunced it on march 2008 soon.

And I would say that at least until iOS4 (2010) the jailbroken version was still better than what apple was doing.