The problem is that if permanent DST becomes the norm, the sun will come up at 9 am instead of 8 am. This means that if you take a 'normal' 9 to 5 schedule, you won't see daylight in the morning.

The researchers here are pointing out the problem that if you do not see any sunlight for the first few hours you are active, that will have negative consequences for your sleep.

I see lots of anecdotal 'evidence' given in the comments that you won't see daylight in the morning anyway. But most people will get to see some daylight during their morning commute, unless they get in before 8. Yes, there will be some days where that still isn't true, around the winter solstice. But outside of the middle of the winter, the researchers point out that it is better to have some sunlight in the morning over having none at all.