I don't see any of the other answers being complete, i.e. describing the reason why bicycles differ from motorcycles.
The difference is the power source: humans versus modern combustion engines / electric motors.
Humans are like steam engines. Humans produce power at extremely low RPM. This results in poor power to weight ratio: humans produce from about fifth to third of a horsepower for a 70 kg human, power to weight ratio being 0.003 - 0.005 horsepower per kilogram.
In contrast, a 100 kg car engine produces 100 hp, power to weight ratio being 1 horsepower per kilogram. Electric motors are even better at this: Tesla's motor produces 362 horsepower for 32 kg or 11.3 horsepower per kilogram.
How do electric motors and internal combustion engines achieve such a huge power output per kilogram? The answer is RPM, rotational speed. Power is torque times RPM. Torque for a car engine is actually quite poor: a 100 kg car engine produces perhaps 170 Nm, or 1.7 Nm per kg. A 70 kg human using shoes that attach to pedals on 170 mm cranks produces 70 kg (weight) + 25 kg (pulling up from rear shoe) + 25 kg (pushing on the front shoe an equivalent amount) + 30 kg (pulling up from handlebar), or 150 kg or about 1500 Netwons times 0.17 meters, being about 250 Nm. So: 250 Nm per 70 kg, or 3.6 Nm per kg. That's more than a car engine!
Unfortunately, humans can pedal at only about 100 RPM. In contrast, car engines operate at up to about 7000 RPM, and electric motors at up to about 20 000 RPM.
The poor torque output of these man-made machines is compensated by operating at huge rotational speeds / RPMs. Humans can never achieve that.
To understand why the gearing is different on bicycles and motorcycles, see the accepted answer: it's all about the RPM. But to understand why the RPMs are different, I think my answer is needed.
By the way, the RPM mismatch is also the reason why electric bicycles took so long to materialize and why even today they are suboptimal. The human wants to pedal at leisurely 60 RPM, whereas a good electric motor would like to spin at 20 000 RPM. The mismatch is usually solved by building a poor electric motor that spins at only 200 RPM @ 25 km/h and putting it to the wheel hub. That's not a problem because these poor motors produce only 250 watts, a fraction of what they could produce if spinning at 20 000 RPM (25 000 watts = 33.5 horsepower). For mopeds (moped means motor-pedal vehicle), the mismatch was solved by eliminating pedals, so despite their name mopeds don't anymore have pedals at all.
Also, the reason why serious cyclists don't use internal gear hubs is the same: the peculiar steam engine like characteristics of humans. I think only the very expensive Rohloff one withstands 250 Nm at the bottom bracket... If the cyclist weighs more than 70 kg, you already exceed that. Additionally, the reason why bicycle parts fail at a great rate and car parts don't fail at such a great rate is the same. I presume steam engine parts also failed often.