This is important. An inside zone play is a second level blocking play....fire off to combo blocks, set, then onto the linebacker. A good zone team makes this look like one smooth move.
In 10 or 11 personnel that's one or two backers to block and then often only 1 deep safety for the RB to beat. In the personnel packages Mav listed, not only is it harder to block the numbers in the box but you're more likely to see a 2 or 3 deep shell, they may crash the corners, etc.
Wisconsin in the second half is an example. They blocked well, we didn't defend well and they were getting more 10 yard runs than 70 yard runs.