I think the value of their main residence is a bigger driver than opportunities through zoning changes. It's easier to sit in your house year after year as it increases in value than it is to go through a redevelopment process, and have to move or end up with a less impressive residence. I'd guess that many would look for opportunities in denser suburbs elsewhere than agitate to change zoning closer to home.

There are strong factors around character of a neighbourhood: I think people in valuable SFHs tend to resent people in units as one example. Housing prices have typically risen without the assistance of zoning changes.