Because the sale of Gucci watches does not push more affordable watches off the marketplace and out of the hands of people who do not have enough money for more.
The issue with gentrification is this: it ruins existing communities and takes opportunities away from people that don't have many to begin with.
People have to move from the neighbourhood they've known for decades with good facilities and schools to an area considerably further away from the job market, bringing down their quality of life and reducing the chances that they'll ever be prosperous enough to live in the neighbourhood they've just been forced out of. But hey, smart, innovative kids will still rise up, right? Well, no, because now they're nowhere near the good schools and after school programs. Neither they nor their parents have the opportunities that others do. It's not exactly the kind of meritocracy Silicon Valley champions.
The very fact that you think these people are deciding to rent speaks volumes. Not everyone can afford to buy a house or get approved for a mortgage. They have to rent, and are increasingly powerless to stop these kind of changes. Gentrification is not all negatives, but are you seriously saying you can't see why people would be angry about it?
We also have other ways. San Francisco's rent control is one such way. It entitles the tenant to continued occupancy and limits the rent the owner can charge that tenant. Of course, this has significant negative side effects. It deliberately fails to respect the owner's interests, instead rejecting him as an invalid actor, some sort of Evil Capitalist type. It effectively functions as a wealth transfer from the owner to the renter, in the form of foregone rent increases. This naturally changes the capitalist's incentives, inhibiting the maintenance of and formation of new capital (specifically the capital we call a "housing stock"), and provides other perverse incentives for the landlord to mess with tenants.
In the case of San Francisco, this housing shortfall exacerbates its problems by raising the price of all housing... a humanitarian tragedy far in excess of mere neighborhood-dissolution. Not that this is the only thing that inhibits homebuilding in the Bay Area, though.
SF does not have an abundance of good public schools. It's not atypical for families with school-aged children to move to the suburbs to afford their children a decent education.
> ...to an area considerably further away from the job market
But it's the techies with the disposable income who are creating a significant amount of the jobs the blue collar workers seek. The benefits from having people with disposable income is not extricable from the people themselves. Else you can have Detroit. That's the end-game.
I don't know of there being a 'right' to live in a particular place. Such that I would have a 'right' to live in Berkeley --whether I could afford it or not. Or Oslo, or London.
Why don't we see people clamoring against the 1%-er actors and actresses in Hollywood? I think people in LA understand that these free spenders benefit the local economy when they spend their money like there is no tomorrow. If the overwealthy actors and actresses in Hollywood didn't spend their monies, then that _would_ be a problem. There's be no infusion into the local economy.