In addition to the answers so far, I like being able to get out of bed and already be standing than have to stand up from the ground to get out of bed.
I used to have a floor level bed, it was actually kind of nice. It’s cooler down by the floor. But it sucks waking up and having to exert serious effort in order to stand.
Like ezraglenn said, having a bed on the floor is colder. Heat rises. And (like Harp said), it is way more comfortable (and safer) to jump in a bed that is above knee level.