Rumors were rampant that Esser was not giving up his jailbreak secret because he did want to be part of the pirating of software that many who jailbreak iDevices are guilty of by using cracked applications. But that is not the reason for Esser keeping his jailbreak to himself, according to an interview he did with the Italian language site Ispazio.net (Google translation link included).
Esser says the real reason he has not released his jailbreak is because the jailbreak community is contaminated by "leeches"; Ungrateful users who harass Esser and other jailbreak hackers for not jailbreaking devices fast enough. Some of these users have adopted the attitude, according to Esser (and I have seen this myself in the comments on jailbreak sites), that these developers would be nothing without the people using the jailbreaks. That the jailbreak community has made the jailbreak hackers rich and famous beyond imagination. Therefore, the jailbreakers owe it to the masses to work night and day on jailbreaking the next version of iOS and getting it out as soon as possible.