The IDF is more specialized in counterterrorism than the US military, but that's because counterterrorism is 70-80% of the IDF's mission--the other 20-30% being defense against comparatively feeble Arab armies. The IDF also only has to defend itself.
The US military has much, much wider requirements--it has obligations to South Korea, Japan, NATO, and the entire Western hemisphere, which demand a strong conventional warfighting ability.
People quote that statistic all the time. Suspiciously, the US also has over 150 embassies, and each of them is guarded by a small detachment of Marines. I wonder what the number really is when you stop counting embassy guard details.
The US military has much, much wider requirements--it has obligations to South Korea, Japan, NATO, and the entire Western hemisphere, which demand a strong conventional warfighting ability.