When they started offering smartcard tickets a few years ago, I suggested to them on their Facebook page that they introduce a 2 journey ticket and they said that they would lose money by people making a return journey for the price of a single. But this is obviously going to be possible with the 60 minute ticket.
It is, but only for someone who is travelling two stops, buying a paper and travelling back (who might only do so considering they've got rather a bargain), or someone who is riding for 59 minutes then straight back for the sheer hell of it (who we don't really need to legislate for - who really cares if a basher gets a bit of a cheap bashing session they might not have bothered with otherwise?)
The big risk of this kind of ticket is passback or resale - associating it with a mobile phone or contactless bank card near enough removes this, or at least to the same extent as a day ticket.
It's like day returns. There is no point legislating for someone using a day return twice if ungripped. Almost nobody will ever have cause to do that, and if they do it won't be worth the financial while bothering about it. Indeed, Merseyrail went the whole hog and did away with CDRs - now you get a zonal day ticket which you can legitimately use as much as you like.