1. First of all, that cheating isn't that common as you say. Most often the farm are old teams(the young team buying most likeyl are screwed and quit and ruin the GS), who lost motivation on the common gameplay like docend for example, but who are willing to help the NT. So this would be a lot extra work with nearly no extra use. Since NT players are public known, it will be also a pillory.
2. The FA fee makes them retire quite often today.
3. it will kill a lot more players, who ain't owned for NT cheating purpose.
4.it will produce the different approach, in sabotage to the NT.
5. it will kill player who are trained a long time from normal user, who still follow them(at least i get some mails from ex owners, if i still develop them or that they like to see them still playing on a big stage) i beleive on NT level this is even more common since team sacrifice them at least a bit for it.