Concentrated vs diffuse costs:

Execs and managers have inherently social jobs, so not having everyone in the office is a concentrated pain point for them compared to it being a minor inconvenience for most individual contributors. Conveniently for the execs, they also have concentrated power to decide this for themselves and ICs, whereas ICs have little collective power.

  Return to normal:

Companies that don't return to office as soon as the pandemic recedes will have a much harder time justifying the move later (see Yahoo!). So if there's a time to dig in and fight, it's right now as the extraordinary situation of the pandemic ends, since whatever policy is in place then will likely stay in place for years after.