After the voltage pulse is dissipated in the gate resistor, the FET turns back "off", its normal high impedance state.
A capacitor may be used to store the charge to lengthen the time constant of the gate circuit and therefore the width of the pulse.
One is that there are no (significantly) moving parts, just the small deformation on the front plate and the piezo element (typically a few micrometers).
This means the lifetime of such a switch can be ensured to be tens of millions of operations, since there is no wear involved.
They are often constructed with stainless steel housings such that they are resistant to damage by vandals or heavy use.