> renters get the same one vote per person as everybody else
It's not just directly voting for a city councilor, planning board member, etc. that counts. Showing up to public meetings to show support or disagreement with something can do much to pressure those elected officials. But renters are going to have a much more difficult time showing solidarity for pro-development action, not only because of the difference in socioeconomic status (e.g. living paycheck to paycheck vs. a homeowner who has a stable, white-collar job).
1. Homeowners can shoot down a proposed development by demonstrating a strong response against threats on just their street or block. As long as homeowners defend their turf locally, and it can be counted on them to do so across town, they win. Renters, on the other hand, have an asymmetrically difficult battle: pro-development individuals need to show up to all the proposed-development meetings, not just one for a particular street or block, if they want to expand housing.
2. Homeowners are probably much more strongly driven to show up because the focus is on what they lose. Character of neighborhood, traffic, safety, noise, etc. and the threat against the status quo seems more likely to trigger that visceral defense mechanism. Renters probably focus on what they gain: affordable housing, access to new communities, etc. My intuition is that the perception of losing something is a greater call to action than the possibility of gaining something.
3. Homeowners are well-defined and known individuals. They already exist, and their turf is already developed. Renters, on the other hand, are an abstract group of people who may or may not even move in, should something be built. I currently rent an apartment - but will I show up to a neighboring town's planning board meeting to voice my support for some proposed apartment complex that's still in the early stages, could flop at any point, and even if it succeeds I may not even move there? The renters of a future complex may not even know who they are yet, if they aren't adamant on moving in there should a place be built.
4. There's strong stigma against renters, to the point of being demeaning and tribal. A local council near me voiced their opposition to building more affordable developments, and the chairman said he was concerned about "derelicts" (exact word) moving in to the neighborhood and said if they built more affordable units, you'd see a rise in street drug vendors, threatening the local children. How can renters and low-income earners combat such ridiculous accusations when local leaders cast them as criminals, just because they can't afford to buy a median $400,000 house?
Your comment ignores so much of the asymmetric power dynamic between owners and renters.