When people talk about "using land productively", they aren't talking about a single person's profit. It's more of a "collective productivity".

You can only pass on so many costs before demand drops because the price you're asking just isn't feasible.

Non-resident landlords in SF, to my knowledge, aren't really anti-development. They recognize that 2x the number of units on the same parcel of land won't cut the per-unit rent in half, so higher density is still a better deal.

The problem, from the individual landlord's perspective, is that they can't redevelop their own land without triggering a tax reassessment, which can easily turn any profit into a loss, even after adjusting rent for the newly-developed property. The landlords who are making out like bandits right now are the ones who have owned their properties for decades. I wouldn't buy a duplex or a quad-plex in SF right now with the intention to rent it out; the cost of the property, plus 2020-assessed property taxes, would mean I'd barely break even at market rates (pre-pandemic market rates; current market rates might be a solid operating loss).

Large developers that are coming in and wanting to build apartment or condo complexes essentially have to build so-called "luxury units", because the economics won't work out otherwise, when you take into account high initial property taxes and the high, drawn-out cost of just building in SF.