Israel really doesn't have a lot of options here. They seem to cling to some hope that Hezbollah hasn't killed the soldiers yet, so they bomb infrastructure to hamper this effort.
Israel does not want to risk more troops, thus its response is limited to a big air and naval operation. There may have been options through more clandestine means, but I do not think the world would respond any better if the Mossad were bombing cars rather than the IDF bombing bridges.
Remember that Israel has not been very well-served by its Lebanese allies in the last 25 years or so.