I think this is a sort of obvious effort at a form of gerrymandering - if the assumption is that the residents of higher-density dwellings are more likely to vote Democrat on average vs the current home owners, spreading high density housing around districts (vs concentrating them in the already-super Blue cities) locks democratic control over those districts with more probability/certainty.
There are obvious concerns being raised about - traffic, ability of utilities to handle the extra density, school capacity, not to mention wishes of those (like me) who explicitly chose a suburban lifestyle for our family - when viewed through the cynical electoral lens these concerns aren't relevant to the decision which optimizes for power concentration at the expense of everything else.
No idea if the same dynamics are at play in Cali.