My (relatively small) refrigerator consumes around 170kWh annually.
According to another commenter further down, a pro cyclist can put out 300W continually. That works out to about 566.6 hours, or 23.6 days of continuous cycling just to power the refrigerator for a year.
I am not a pro. The last time I seriously tried to use an exercise bike, I was able to keep a steady ~110W over 45 minutes (which left me drenched in sweat and feeling jittery for quite a few hours after the fact). That works out to 1417 hours, almost exactly 2 months, which I would need to spend on the bike at my absolute limit per year to keep my refrigerator running.
And of course, none of this is taking losses in energy transmission/storage into account. In short, I don't see this catching on any time soon.
Wouldn't I need to buy two more bikes and people to pedal them to power the first bike? What if I start a gym that's only focus is cardio and then resell that energy the people nearby.