But if I had to hazard some guesses I think it is going to boil down to over confidence on the part of thier intelligence agencies and ground forces.
1- The majority of thre troops used seemed to have been reservist who cut thier teeth vs Palestinians led by commanders who learned their offensive skill in the 80's cutting through the PLO and hezzies in Beruit. Or regular troops who have been sititng instatic posistions since the last lebanon war ended. All raised on Israel's tradition of victory and elan.
When they ran into a foe that was every bit as dedicated, smart, and well equipped, a foe that just a few years before had not been any of those things the IDF unravelled.
The IDF has never really repsected the Arab fighter. They reserved that for the Egyptians and Jordanian's. These reservist have been imposing Israels will on the West bank and Gaza vs gunmen and suicide bombers. I don't think they were prepared for the tenacity of the Hezzie fighters.
Hezzbollah knows how to recruit and indoctrinate fighters who will sacrafice thier lives. They then spent the last several years mating that fanaticism to the following. Modern anti-tank missiles en masse, a defensive net that was fully autnomous and didn't need higher levels of control, superb camoflauge, and an excellent media corps.
2- Iran/Syria supplied the Hezzies with advanced anti-tank weapons. We all remember Israel complaining to Russia about Kornets and RPG-29's. This points to the failure of the itnelligence agencies. The ground troops thought they were going to be facing the same O same O and felt invulnerable. I think they made the same mistake they did in 73. They felt thier tankers were the best and could take on any threat and so sent them in unsupported.
I recall one of the worst losses for the IDF was the initial rescue effort when a Merkava doing duty as a tank and as an IFV ran over a Hezzie mine and got imolated. Mines should have been the last thing to take out a Merkava in a border area. It points directly to over confidence beucase you know the border will have mines and engineers should have been in support.
Later as the war progressed and the Hezzies in the towns refused to break, this pinned the IDF in place. I think the Israelies failed to set up proper op-sec and this allowed the anti-tank teams were able to come into play. The video out there that shows an IDF tank getting hit repeatedly is almost certainly staged. The truck off to the tanks side is already fully involved (on fire) and tank is not moving or scanning. I think a command detomated IED or earlier ATGM got it, but the fact that Hezzie missile troops and cameramen could move about in the open daylight and shoot a tank form multiple directions shows Israel did not have command of the aproaches and high ground.
Hezzbollah could not command, counter attack, or resupply but it's light infantry anti-tank teams operating form the supply bunkers were the weapon with the most mobility in the recent war.
3-All that said I think a certain level of shock set in as well. By the time the overconfidence wore off and adaptation should have set in, The IDF drive flat out bogged down, but losses didn't skyrocket. This to me implies a certain fatalism among the troops and an unwillingness by commanders to press the attack home. Isreal knew she had to win or play the fool on the worlds stage and despite this her troops failed.
In closing it looks like the local commanders tried to bus tinto Lebanon ealry and resuce the troopers who were snatched. A repaly of Peace of Gallilee but on a smaller scale. The problem was Hezzbollah had been planning to fight just that kind of operation. Like Gettysburg or Stalingrad the IDF started feeding troops into a battlefeild of its enemies choosing and never gained any traction.