I wonder why tech companies aren't allowing the option to change from full-time (100%) to part-time (60%), while retaining all the benefits especially healthcare in the U.S.

This can help ensure that everyone is being measured fairly - for example parents can opt to change to 60% and their role/responsibilities will be adjusted accordingly. Management will be able to hire to fill the gaps. Conversely if you're a parent that opts not to change to part-time and fails to deliver per the full-time expectations, then you get a "NI" rating or PIP.

Seems like this might normalize the compensation/recognition dimension at the heart of this debate. For parents that feel they can't stomach the pay cut from the switch, then there's no option but to work nights/weekends.