Well, there are a few differences between the hack and regular squats. A big difference is that while both the hack and standard back squat work the quads, the standard squat also works a few other muscles, which can make it more of a full body movement. Here’s an article on Livestrong that talks about this in more depth: https://www.livestrong.com/article/538392-a-hack-squat-vs-a-back-squat/