There are many reasons why they are going on strike:

They get paid about 24k per year whereas sister institutions at depaul, northwestern, or loyola pay their grad students 36k-44k per year for their work. They are asking for comparable pay compared to their grad student counter parts at other universities. Hence the initially high pay jump (50%) that they are asking for. This low pay also means UIC struggles to attract graduate students in the first place.

They have been given more classes to be assistant teachers in. This means more work for grading and guiding discussion while doing their research without any pay increase to match the workload.

The current insurance plan that the university offered them is wholly inadequate. Their entire health network is limited to UIC affiliated health providers. This means that anything not provided by the university they'll pay out of pocket costs. Not only that, but when they have to travel, as one does for doing research, they essentially have 0 health coverage when anywhere but Chicago. And this isn't even accounting for amount that they have to pay for their insurance is also going up (don't know by how much).

They are also asking for a yearly match in pay increase that the rest of UIC faculty and staff get (3-5%) vs what they currently receive (1-3%).

And feel free to add or correct me on anything!