Indeed. At a local nuclear power station there's a visitor center where one can experiment how to generate electricity with an exercise bike. With moderate power you can power a tablet computer or an incandescent light bulb, but the water kettle comes on only with actual athletes, and even then, the small light bulb goes off, and even a professional cyclist can't sustain that power for longer than a brief moment.

It's just pointless to generate electricity by human power. It's not pointless to ride a bike.

Not to mention that a Tour de France Athlete is consumed during the Tour. You need to accumulate reserves for at least three months in order to last 23 days of effort.

It takes an Olympic Cyclist mashing until he has to lie down just to make a piece of toast.

https://www.youtube.com/watch?v=S4O5voOCqAQ

On a good day my house uses 8kwh, I suppose I'd qualify as an endurance athelete after pedaling 20hrs a day for a bit.