I'm sorry but it's not wrong. It's standard practice at most sporting/concert venues.
The reason is when start getting big ques the people paying cash hold up the que and lots miss the start of the game. Having worked the turnstiles several times at Barrow, it's absolutely hellish on a busy match as you cannot process that many cash transactions in 10/15 minutes just prior to kick off.
A system where you can let people in and no one is paying should mean that there are only small fast moving ques at the turnstiles.