They've been on sale for 2 weeks, and on general sale for the past week, and the allocation hasn't sold out.
That indicates to me that they've got the allocation just about right for this one.
It's the 3rd game in 5 days, on a weekday night, involving a round trip of 340 miles/8 hours from Liverpool, necessitating a half days holiday (at least) from work, and getting back to Liverpool in the middle of the night. People also may be saving up for trips to Lille and/or Wolfsburg. You really can't blame people if they have to give this one a miss.