Because it's a lot more people I'd guess. You might get 50-100 people turning up to a pub over a period of time so it's not the most difficult task to get them to leave a number but you wouldn't want 13,000 people turning up at the gate at quarter to three who we have to collect contact details from. I think we can agree that tickets will be scarce and people should use them if they're lucky enough to get them. I don't particularly have a problem with people passing them on, as that's better than the ticket not being used. But people will have to accept they'll have to provide their contact details in advance of arriving at the ground.
The price of getting people in stadiums is that the government, PL and SGSA will insist that clubs know exactly who's in the stadium and how to contact them if required. If they can't then it's quite possible it'll mean no fans at all are admitted.