Why did humans evolve big penises but small testicles?

We have the penis of a monogamous primate yet our body sizes suggest our ancestors slept around a lot.

Penis evolution across species: divergence and diversity

Why DO humans have such large penises?

i.guim.co.uk/img/static/sys-images/Guardian/Pix/pi

Why did humans evolve big penises but small testicles than other apes? - Quora

Why Did Humans Evolve Big Penises But Small Testicles?

Is Penis Size Genetic?

Is the human male's penis size being bigger than other primates an evolutionary thing? : r/evolution

Evolution – Notícias, Pesquisa e Análise – The Conversation – página 30

Why Did Humans Evolve Such Enormous Penises?

Lesson Explainer: Male Genital System

How come you never see any gorillas who are hung like a horse below the belt? - Quora

Beauty and the Beast' Features Disney's First Gay Subplot - Gayety

Why DO humans have such large penises?