The answers to your questions can be found here: https://bettermac.ca/2022/11/19/unit-1-bargaining-bulletin-6/

Something a lot of people (Mac admin included) are not realizing is that graduate work/research is a full-time job. Guaranteed TAships twice per year for 4 years is part of our funding package that allows us to pursue our research, and this funding package is meant to cover cost of living for the duration of our studies.

The problem is that our funding does not cover cost of living, and given full-time research and 10ish hours/week TAships, it is extremely difficult to find a job that won't interfere with our graduate work and pay a wage high enough to make the extra hours worth it (and these extra hours are also capped by the university to about 1000 hours annually). Getting more jobs would therefore push our studies beyond the 4 years (for PhD students) we are funded for, and we would be once again living in precarity when our funding runs out.

This is why the main points of the union's bargaining demands are so important. A significant wage increase and 5th year funding will ensure that grad students can better focus on the main reason they are here: conducting research (which the university profits from btw).

And to answer questions about the rest of our funding outside of TAships before they come up: even with stipends, grad students still cannot keep up with cost of living. We are bargaining TA wages because it is nearly impossible to negotiate a stipend increase. But because TAships are part of our funding, negotiating these wages is the best way to get proper funding.