Why do 18650 batteries with lesser capacity (mAh) produce higher Amps?
The energy density (capacity per volume) of a battery is a result of chemical and structural requirements which stand in direct contradiction to power density (I.e. high current capability per volume). Those being primarily high electrolytic volume vs high electrode surface area.

Also, high-current leads to high-temperature. And that is all the riskier the higher your capacity is - hence, reliability and ruggedness is another contradicting requirement.

Of course, cost plays a role, too.

Thus, it's either very expensive or impossible to get high-capacity batteries that are also high-current.