I've helped a lot of people to set up new phones and saving WhatsApp chat history is always low on their list of priorities. Keeping their contacts, their photos and all the saved logins for websites and apps are the top 3.

Wiping the WhatsApp chat history on the old phone before giving it to a new owner is also much more important. It often contains highly embarrassing or even incriminating details.

wouldn't it be advisable to do a factory reset on an old phone before giving it to someone else? There is a lot more personal info on there than whatsapp

Maybe so, but it doesn't benefit either platform.

It may not _favor_ either platform but I'd say they both benefit.

In ecology, it's rare to species compete to extinction or exclusion from a niche. It's much more common to observe segmentation. It's a lower energy state for birds to mate at different times, eat leaves from different parts of the same tree, etc., dividing the resources of their niche among themselves, than to force each other out of the niche completely.

The situation is analogous. I'm sure they'd destroy each other if they could, but it's obviously not happening right now. It's much easier to say, you can have your current users, we'll have ours, and we'll focus our energy on capturing emerging markets. Which is why you see them racing to provide free internet to developing countries and such.