The quads are also hit somewhat with the deadlift walks, but…
Remember, this is not a bodybuilding program - and unless you’re a bodybuilder, you probably don’t need to worry about hitting the quads too hard. Most people would do well to bring up their weakest link, usually the posterior chain, and this program does just that. Remember, it was originally designed as an in-season football program.
just an aside with regards to Overhead Squats. One of the important components that you have somewhat backed-into commenting on is the strength/stabilization of the shoulders when performing the life and how the load is too light to really impact upon your legs. I would suggest that in within your use of Overhead Squats you also make use of the Snatch Press and the Muscle Snatch Complex to help bring that weak along. In time this will help you to really drive down/away from the bar with a much more significant weight.