Animal desires are naturally dealt with in the world, on a moment to moment basis. The Buddha's Middle Way recognizes the naturalness of desire and its satisfaction. Pleasure and pain are the life forces that regulate action in relation to natural drives. Leading to satiation after satisfaction. They are variable according to metabolism and chemistry generally.
Pleasure is to an extent socially determined as well.
Conditioned through culture. And hence pain too. Nirvana is not heaven on earth, nor beyond rebirth. Ever-present happiness is a delusion. Natural suffering from natural pain continues beyond enlightenment.