CS PhDs here have it relatively good, at about $55K / year before taxes, but it's still common for us to spend more than 30-50% of income on rent. (Even in shared housing, it's very difficult to find anything cheaper than $1.3K / month.)
I do know that for students in other departments, money is extremely tight, and they often have very limited options and periods of housing insecurity. As a side note, the homelessness problem in Berkeley has gone from bad to insane over the past few years that I've lived here. I essentially never leave my house, in a pretty posh part of Berkeley, without an uncomfortable interaction (homeless people in various states of undress, under the influence of drugs, talking to themselves, or screaming).
Meanwhile, the UCs (and UC Berkeley in particular) continue to expand a very expensive bureaucracy (I question how many $500K/year vice provosts we really need). It's not that they don't have the money to pay grad students more, but that they're not incentivized to allocate it towards making grad students' lives better.
Unfortunately, there's an apathetic attitude among many students on campus of, essentially, "doing your time and getting out," since they know, at least in STEM, that there's a pile of money waiting on the other side.
It will be interesting to see what happens over the next few months and whether the COLA campaign expands to other UCs. The UC administration is very fearful of union organizing (as evidenced by the many weird anti-union emails the university sent out in 2018, during the last contract negotiation).