Why did the Penny-Farthing require a massive front wheel to achieve speed?

Pedals were attached directly to the hub of the driving wheel

The Penny-farthing operated on a direct drive system where the pedals were fixed directly to the axle hub of the large front wheel, which served as the driving wheel. In this setup, the distance covered with one revolution of the pedals is equal to the circumference of that wheel. To achieve any meaningful velocity suitable for novelty or speed, engineers were forced to maximize the wheel's diameter. This mechanical constraint—the reliance on direct linkage—was the specific reason the iconic, massive front wheel configuration became necessary to achieve reasonable speed, even though it severely compromised rider safety by elevating the center of gravity.