Probably because of the fact that he couldn't cut it in the OHL, and came back after one game, before upping sticks from Kazakhstan in pre-season because it was too tough for him.
And that's secondary to the fact that... he's not all that good?
None of this is even true. It wasn't because he "couldn't cut it" in the OHL. He was an import in the OHL and you have to be really worth one of those two spots, if he was Canadian he would have cut it in the OHL easily, a Czech defenseman became available and his team decided that guy was a better option.
It probably wasn't the hockey that was too tough for him, he was in a country where not many people speak English and yes while Ben O'Connor was able to stick with it there, some people are just better at dealing with the culture shock. I've just come back from spending 2 months in Russia after living a completely sheltered middle class life in South Wales/England, it isn't easy, after a few weeks I was thinking "**** this **** I want to go home"
Farmer is a good player, while other guys may be more skilled than him, he is much better suited to the North American style of play on the smaller ice.