The official reason - a trial period before the final arrangement, whatever it is. To see if the "peace" holds etc.
The real reason... I'll give you a hint - almost exactly two months from the date of ceasefire a certain Orange Man is going to assume a certain very important Office. Of course, by a completely surprising coincidence two months happens to be the duration of ceasefire.
That will open a range of possibilities, which don't exist right now. There is a talk in town about creating a buffer zone along the northern border, preventing the return of residents to the Hezbollah aligned Shia villages and making them permanently depopulated.
IDF also badly needs a break - especially the reservists, which is the bulk of the fighting force. Also, IDF needs to replenish its ammo stockpiles - those JDAMs and
explosives used to demolish the Hezzi infrastructure don't exactly grow on trees. Not to mention the quite embargo by the Biden admin, which also takes it toll.
So this is the rationale in the nutshell - Israel takes a break, sacrificing virtually nothing, possibly accelerates deal with Hamas (Hezzies out of equation, Hamas loses its last real leverage, beside the hostages). If the gods of peace bestow upon us their grace - great. If not, with Trump in the office new course of action will be considered with new options on the table.