There's no such thing as an invulnerable tank. In warfare this century tanks have been among the most vulnerable weapons...particularly in urban areas. The Marines have a saying..."Killing Tanks is Fun and Easy." Tanks have serious visibility and maneuverability problems in built up areas.
It's only the media acting like losing one tank is some sort of shock or crisis.
Traditionally, tank losses in battle are enormous, but fortunately the loss rates among the tank crews are fairly light, typically...at least some, or often all, of the crew escape a destroyed tank.
The Israelis lost plenty of tanks in the 1973 War, for example. They haven't had enough really serious full-scale combat since, to lose plenty of Merkavas, since they were developed after that war.
I'm certainly no weapons expert. My 8 years of active duty military experience was in the medical corps. However, if these tanks were so vulnerable before, why is it that no one destroyed them until two were destroyed within the past week? I'm not talking about past losses but the losses of the current Merkavas. This represents an escalation of military loss by the Israelis regardless of the mechanism of loss. That is, the Palestinians, or whoever is fighting with them are now able to accomplish something that they wer unable to accomplish before. I don't think these events are inconsequential.