Long Rest does not mean sleep. It means light activity. Reading, memorizing spells, etc., all occur over that 8 hours. This is realistic and 5e rules.
The point of 2 Long Rests per day is that right now it makes even less sense to Long Rest because it is only 1 per day. I only adventure maybe 1 hour at a time at best and Long Rest meaning End Day. So adventure 1 hour, rest 23? Makes no sense when you are supposed to be racing against time before gobbos attack, etc.
At least with 2 Long Rests per day it is adventure 1 hour, rest 8, adventure 1 hour and rest 8. That's 18 hours. Add 2 short rests per Long. Each short rest is 1 hour. That's roughly 4 more,hours for a total of 22 hours per day. This gives you roughly 2 extra hours per day that could be simply accounted for by saying some rests were longer than others, or you could maybe adventure more than an hour before each Long Rest. Either way, more believable.
