The rivets had a head. Ok, many locks were of the horizontal style and maybe wire could be used on these but it would have been a pain to try to keep wire in place on a vertical lock.
There's also the fact that the clenching pliers would need to be able to open quite a bit further.
Regards, John...
Huddersfield, best value for money in the country, spend a day there & it'll feel like a week........