Its basic evolution - any successful species is programmed to increase in numbers. A species that aims to stay static will die off when conditions change, and of course one that aims to shrink in size will not last. The cancer word is just clickbait.
A species that grows so much that it outgrows its own habitat will often end up destroying said habitat due to overpopulation, with ramifications usually going way past the species that actually triggered it.
That's why not everything that is natural is automatically "good"/sustainable.
Because if we go about it that way we might as well never have come down from those trees, as humans we can think ahead and conceptualize possible long-term consequences of our actions. That's an advantage not many animals have, we best make some proper use of it.
Evolution pressures reward adapting and surviving. Unlimited growth is fatal. Bacteria in a closed jar will consume all resources put inside then die out.
Sentient species can learn to limit their consumption to maximize their survival.
