Because that way they'll become wards of the Iranian state instead of the Israeli state? Generally when Israel makes these "A Single Israeli Boy Is Worth 1,000 Palestinians" swaps, the released terrorists and murderers have to sign oaths saying they won't go back to terrorizing and murdering. Apparently Israel isn't sure they'll take those seriously:

Israel prefers to release Palestinian prisoners to the Gaza Strip rather than the West Bank as part of its swap with Hamas in exchange for abducted Israel Defense Forces soldier Gilad Shalit, Army Radio reported on Thursday. Defense officials fear that freeing the jailed militants into the West Bank could weaken Palestinian President Mahmoud Abbas and strengthen Hamas in Fatah territory, the radio said. Israel also wants the authority to determine which of the prisoners will be released to Gaza and which to the West Bank, the radio said.

Not the worst point: what are they going to do in Gaza? Ruin the place? Even rich Gazans - are heartbreakingly unable to find solace in their Rolexes and Ray Bans these days. Except for the whole "they'll go back to being terrorists and murderers" thing. That might be a sticking point. Although it looks like freed Gitmo detainees are about to corner that market anyway:

Revisit the exit question to that post. If Roggio’s right — and I say if because I’m not sure how he and Nibras Kazimi can be so sure the guy in the vid is the same Abdullah al-Ajmi — then the poor dear’s choice of target to supposedly avenge the hard time he had at Gitmo was curious indeed. 13 dead, 42 wounded in a truck bomb attack … on an Iraqi Army base. So much for grievance.

Super.

References:
* Report: Israel prefers Hamas prisoners be released to Gaza, not West Bank [Ha'aretz]
* News Report from Gaza: "Mr. Gosh's Rolex, Ray Ban sunglasses and tailor-made Italian clothing provide him no solace" [BtB]
* New Al Qaeda truck bomb video features … freed Gitmo jihadi [Hot Air]

Previously:
* Gilad Shalit Is Alive, Forced To Say That Hamas Is Letting Him Die (Updated: Shas Leader Calls For Direct Prisoner Talks With Hamas)
* Abbas: Hamas Will Free Shalit Soon. Hamas: No We Won't.
* Palestinians Say They Won't Release Shalit Because of Qana - Asks World to Forget That They Weren't Going to Release Him Anyway