I’m an adult educator myself. I’ve been working with adults to acquire their high school credentials for 13 years.
I would say that most adult learners are not intrinsically motivated to learn their high school subjects; i.e. they don’t learn for the fun of learning. They see their high school courses as means to get into the programs they really want to be in, such as nursing or engineering.
Regardless, the ones with an end goal in sight are usually motivated enough to do well with high school material. Those without some kind of end goal tend to flounder.
And yes, I am amazed at how the better students juggle job/family/academics. We often see some students taking on too big of an academic load for where their life is at.