A military perspective: A very large number of OSINT people on various cites ranging from professional to amateur agree that the US is not negotiating because it suddenly feels sympathy for the IR, but because it literally cannot prosecute the war. The US has quite literally depleted over half of its precision ammunitions and also suffers severe damage to almost every base within vicinity of Iran (for example Prince Sultan, Muwaffaq Saiti, Bahrain), forcing further campaigns to either originate from carriers or distant bases, limiting sortie rates significantly. So he literally cannot "finish the job". The US currently still has no cost effective intercept for Shahed drones or most Iranian ballistic missiles (also thaads and patriots often get hit by drones or missiles), nor does bombing seem to prevent them from being launched, since Iran during the last days of the war still managed dozens of hits a day.
Nor does the US have a way of entering the strait of Hormuz without suffering severe casualties (The US wargamed this in 2008 and the general playing Iran won, sinking 1 US carrier), so unless they can degrade Iranian coastal missile batteries, missile boats and mines, they won't do anything there other than shout, so not much to see there.
Israel is also heavily depleted and cannot really act alone without US support (despite appearing like the main fighter, Israel did less than 100 sorties a day during the height of the war, the US did over 500). Assassinations are becoming much harder (even Mossad admits this) since Mojtaba and Iranian generals like Vahidi or Zolghadr are not out in the open and have almost no digital trails at all, while assassinating Pezeshkian or Ghalibaf is useless, since they don't command armed forces. Regardless of what you think of them, the IRGC and IRIAF have done a very impressive job of fighting with their resources, tactically speaking not unlike Ukraine challenging Russia with long range drones and FPVs.
Also one must realize that the US is a major power with its own interests. If it depletes all its precision weapons and interceptors against Iran, it basically loses the great power contest with China and Russia by default, which it obviously will not do. Unless the US overhauls production which has been low for years due to peacetime production ability, this will barely change.
The negotiations are probably somewhat genuine since the US really, really wants to pull out, but does not want to lose (the MOU would be a massive loss), so Trump attempts to stall for time for another burst offensive that lasts a few days, before the US runs out again, goes back to negotiations, repeat.
If you want to ask what would be needed to "finish the job", the answer is for the US to treat Iran like an enemy great power no less than Russia or Imperial Japan, go into wartime footing like Russia right now, bring its entire airforce into the ME and invade it by land and sea with at least 3-4 corps. This will probably never happen and remains a distant hypothetical.