If there is another thread on this subject, then feel free to move this or merge it or whatever needs to be done. I didn't see anything when I searched so I thought I would make this here.

My question is, why do Pokemon lay eggs? Not the how, but WHY. As I have said in other threads, I just watch the anime, and I look at the franchise from a story perspective. Now I know since Pokemon originated as a game targeted at kids, Pokemon had to lay eggs since that's better for the audience than the other means of reproduction. But that's an out of universe explanation, I'm talking about in-universe.

Think about it. If you look at Pokemon as living, biological creatures (okay, ones with super-powers, but whatever), why do they lay eggs? In the real world, birds lay eggs, reptiles, lizards, and amphibians lay eggs. Bugs lay eggs. For Pokemon based on bird/reptile/bug biology, egg laying doesn't seem too out of place. But with Pokemon, all of them lay eggs, even the species clearly modeled on mammals, like Ninetales, Growlith, Tauros-Miltank, Eevee, so on and so forth. So why do even the mammal-like species lay eggs as opposed to the usual way of reproducing? Not that there's anything wrong with eggs, but form follows function, so why did they choose to lay eggs over any other method, especially when egg laying is really uncommon for mammal biology.

Now to be fair, there are mammals that lay eggs in the real world. That would be the Platypus and all forms of Echidna. These are all native to Australia. From what I read about them, I could see any explanations as to why they went that route either.

So what do you think? Why did all Pokemon adapt to lay eggs, even the mammal-like ones?