The more invasive methods are more reliable, even when compared to perfect use of the less invasive methods.

You can owe the mob 5 sheep. Which means that if you want to have 2 sheep, you'd better buy 2 sheep so you can pay your debts before you start farming wool.

And you can have 1 2/3 pizzas, because you bought two and then ate a third of one.

Sure, you can't have -pi hamsters, but if you have a circular sheep pwn, then you'll need to have pi times twice the radius of fencing, otherwise your sheep will escape.

It's also worth noting that colourful mating displays aren't useful to mammals because most mammals are colourblind. And since bright colours are expensive, and tan/brown/black/white does a perfectly good job of camouflage, there's no advantage for mammals to have the bright colours.