Arnold Schwarzenegger did not skip his leg workout. His leg day was extremely intense. Anybody can do the exercises, but not everybody can do his routine and turn their legs into jelly.
Arnold had an exceptional tolerance for pain and he was committed to exceed the limits of his body. Not only did he use heavy weights, but he increased the sets to stress the fibers and to exhaust the endurance capacity of the muscles.
In his prime Arnold did at least 20 sets for his legs and performed his repetitions until muscle failure. The mistake most people make is that they save energy in the beginning sets, because they know that they still have 14, 10 or 6 sets left to go. Arnold grew his thighs to enormous size by this high-volume approach with heavy weights and the ability to go all-in every single set.
Not only physically be prepared to go the distance, mentally you have to accept that your muscles will be in a world of pain. This means that when the fatigue sets in, you will have to break your mental barrier and not give up. Having a training partner around to push you to handle more weight or to grind out the reps can be beneficial in this case. You can exhaust your body to the ultimate limit with somebody checking on you.
This type of high-volume routine will be exhausting in the beginning weeks, because the body is definitely not used to it, but after 6-8 weeks your body will start to adapt and you will notice the enormous progress in your legs. Nobody will be able to accuse you of skipping leg day. Just make sure you perform all the exercises technically correct to prevent injuries.
Below is an example of a routine Arnold would do. Source: Arnold Schwarzenegger’s Blueprint. The recommended rest time is 45 seconds after each set. Exercise A&B are super sets and ought to be done in combination with each other with no rest in between the two exercises, only after each super set.
To shock the muscles Arnold would sometimes switch squats with leg press and load the machine up as heavy as he could.