On weekdays, early in the morning, your body will already be a priori tuned in to accumulate energy (After all, there is a hard day ahead and your brain knows it very well).
That cannot be said about the weekend. There he is sure that you and I will always find time to lie down and replenish the balance of lost strength, so there is no point in getting enough sleep.
I think it's not about the alarm clock or the day of the week, but about the attitude to work. If your job is not pleasant to you, you don't want to wake up to it. And on the day off, you get up free from this burdensome idea of going to nasty work, so get up. Perhaps you are also waking up because you have fun activities planned for the weekend that inspire you to wake up.