Contract terms lengths are structured so the network will turn an overall profit from your channel. High volume channels pay off very quickly and don't require a long term contract to be profitable. If you're doing 300 views per month, then you might have to sign for 2-3 years for a network to make money from you, so for smaller channels, it's totally understandable, but not something I would ever sign up for.
My biggest problem with a 3 year contract is that the network is telling me that I won't be worth more than I am now in 3 years. That's rather insulting. 3 years ago my channel didn't exist. 2 years ago, I was only getting around a thousand views per month. So a long term contract signed back then would insure that I would be getting paid the same as a channel with 1 thousand views per month even though I'm over 1 million views per month. That isn't good incentive for me to keep growing my channel. The best way to keep both sides motivated is a very short contract. A 6 month contract insures the network will work their asses off to keep me there when it's time to renew in 6 months, and I work my a** off because I want to renegotiate my deal to get paid more. Win win on both sides.