They watch because that particular region is a powder keg that the West are mindful not to inflame again. It's an Arab playground and Israel are playing a dangerous game because the US, whilst a quasi-ally on paper, won't dream of sending forces should the rest of the Arab world be antagonized to the point of retaliation. If Gaza is "cleansed", as Bibi and the rest of his fascists want, Israel would have made negligible gains and more enemies in the process.
As I say, they're playing a dangerous game.