Absolutely. Upzoning never forces owners to "give up their home"-- maybe the issue is owners don't want their neighbors to be able to sell their homes to developers either.

That's absolutely it. People not only are unwilling to sell - as in their right - but also insist that everyone else be unwilling to sell. If they are willing, the permitting process is made to be as painful as possible, in an effort to discourage everyone involved.

Not necessarily true. An upzoning will likely increase the value of the land, which will result in higher property taxes (assuming this is a normal city with no prop13 nonsense).

The higher taxes could effectively force a land owner to sell their property.

Often part of what existing land owners are fighting for is preferential zoning which artificially keeps the "highest and best use of land" a low density detached house, which keeps land values relatively low.

This is assuming no or poor homestead exemption.

I think the point is: what if they don't sell it, at all?

Kids move out of the house, parents retire at 65 and live to 85+. That's 20 years, a whole generation.

If the developer can get permission to build 3-5 story apartments on the lot, then their land suddenly becomes way more valuable than the single home ever was. Most retirees will gladly sell and live in luxury elsewhere. If a few don't, it won't make a difference.

  If the developer can get permission to build 3-5 story apartments on the lot

wouldn't that only work for a single unit? Like, yes, if inside a single-family-zoned block a unit would get a special permission to be the only one to build high density, sure that piece of land would be more valuable than before.

But if the whole block gets rezoned, then there's a race to the bottom.

Other comments mentioned that NIMBYs don't want their neighbours to upzone either.

Many single family home owners will strenuously object to having a developer build a 5 storey apartment building next door because they don't want additional noise, traffic, and people looking down into their private back yard. It directly impacts their quality of life.