Do explain. Also, unlike e.g. Intel who got a huge fine from the EU for price deals with OEMs, Facebook didn't use dirty tricks to gain market share.

Lying about their capabilities and intentions when buying WhatsApp doesn't count?

Having a lot of customers isn't a monopoly.

Having the great majority of the customers IS a monopoly. And also trying to buy the rest is (e.g. instagram, whatsapp).

But then every firm that created a new product or new product category would be immediately illegal.

That's why monopolies aren't illegal, not even in the EU. They have to engage in abuse to create or maintain a monopoly.

But Facebook hasn't done that. Buying your competitors is not abuse of market position, they willingly joined forces.

How so?