Yes, pretty silly for the many posers.
But for many roadies, the laudable goal is to ride far and fast under your own steam. In which case, streamlining by crouching in lycra becomes your best defense against your greatest nemesis by far at speed — air resistance.
Above
crossover speed, the reduction in drag area (CdA) obtained by swapping baggy street clothes for sleek lycra can result in a significant reduction in total resistance. (See Wilson and Schmidt, 2020,
Bicycling Science, 4th ed.) Since drag is proportional to CdA at all speeds, the benefit adds up over the miles and can be parlayed into greater distance, faster average speed, or reduced fatigue.
Just like a motor does.
You don't have to be riding the Tour de France for this to make good sense. What doesn't make sense is to assume that the roadies are wrong about everything.