Employee demand will matter to the extent that there's some level of employer supply in the market. If most employers hold the line, there isn't much for employees to choose from, unless they're one of the very fortunate few who have the luxury of deciding not to work until the appropriate opportunity comes along. If large numbers of employees can't afford to hold out for better WFH policies, then plenty of companies won't need to offer them.
The thing is, a lot of companies are offering 100% now. There is a shift going on. It probably won't be a particularly big shift until larger companies get on board, but it's still moving the status quo little by little.
If so then you're absolutely right. If there ever a small % offering 100% and a larger % offering hybrid, that could be the lever that shifts the boulder.