I understand the basics now.. the ISPs would be like Microsoft/Sony making you pay to use online on their console.
You could argue that Microsoft/Sony are not quite as bad, since they simply make you charge for their own service. ISPs could make you pay extra for the right to use
someone else's products.
How long have ISPs been able to do this? Why haven't we seen it in practice yet?
My understanding (which may be flawed - I have some interest in American politics, but I don't follow it too closely) is that there is currently a debate as to whether net neutrality is the legally enforceable or not. There was
a court case in DC Cir. in early 2014 that concluded it's not enforceable due to the FCC's limited authority. This largely popularised the subject.
I imagine one of the reasons people haven't been abusing this potential loophole yet is that it's not common practice - many countries of the world have specific laws protecting net neutrality, so general industry practices tend to follow. However, since the topic is fairly fresh in the US, the situation could change any moment, which is why securing legal protection of net neutrality is important.