For MOSFET gate drive, it's the transition that draws current, not how long the logic is high or low. Because you need a short high current spike from the driver during the logic transition, you need a capacitor with good high frequency performance, able to take charge and give up charge quickly.
In above example with 200 nsec transition, the effective series resistance of cap needs to be measured at a test frequency of 1/(2 x 200 nsec) or 2.5 MHz, not the 25 kHz switcher frequency.
Most electrolytic caps do not have good ESR at such a high frequency.