I'm not sure if its universal, but in my district the biggest reason - or at least the most often stated challenge to changing the times for high school - is that we have limited buses that service the high school first, then middle and then elementary.
I would wonder whether anyone who willingly created such a backwards schedule could be fit to run a school, except I've met the people who run the public schools in this country...
Even the article states: "We show that a delay in the high school start times from 7:50 to 8:45 a.m. had several measurable benefits for students".
In my experience at least, high school in the UK doesn't start earlier than 9am and usually starts at 9:30am. End of day is about 3:30/4:00pm.
What's the reasoning for starting to early in the US?