Here's why:
* Resource limitations: Larger animals require more resources (food, space, etc.) to survive. Their offspring also require significant resources for growth and development. Having fewer offspring allows parents to focus more resources on each individual, increasing their chances of survival.
* Parental care: Larger animals often invest heavily in parental care, providing for their offspring for extended periods. This requires more time and energy, making it more feasible to raise a smaller number of young.
* Life history strategy: Larger animals often have longer lifespans and slower reproductive rates. This is a different strategy from smaller animals, which typically have many offspring and a shorter lifespan.
Exceptions:
There are, of course, exceptions to this rule. Some large animals, like whales, can have many offspring, while some small animals, like insects, may have just a few.
Ultimately, the number of offspring an animal has is influenced by a complex interplay of factors, including their size, their environment, and their evolutionary history.