f I recall correctly, lots of things are decided by a 2/3 majority
votes on bills are 3/5 in the house, simple majority in the senate.
over-riding a veto, passing ammendments to the constitution, etc, require 2/3. That kind of majority is reserved for the seriously important things, and is meant to ensure that it's difficult at best to pass.
Also, as voters, we should then hold our constituents accountable if they are "playing politics" and not working with both sides to get things done.
I believe that we, as voters, have no constituents. But I know what you meant. As far as playing politics...how else do you get something done, especially if you were to require a 2/3 majority. You'd end up with bills that do nothing, which might be a good thing, because while most folks would compromise nobody is going to go against what they believe in.
"I'll vote for the airplane contract in your state if you vote for the highway construction in mine" might be playing politics, but it's how you get things done, especially when there's a handful of other states essentially competing for the same contracts.