Maybe Facebook team are yet to fully understand bitcoin and hence they are dealing with altcoins for now, later on they can get on with bitcoin. Without bitcoin no other coin really make sense, except one wants to introduce scam to the public.
I don't think, they are a big company and very profitable and they are involve in tech business so I don't think they aren't aware about bitcoin.
They are planning to launch their Libra coin as they want to beat all coins that are use for online transactions for payments and etc. but the government are requiring them to comply with the regulatory requirements, once they were able to pass that and launch their coin in the market, it's guaranteed that they will be very profitable as they can use their popularity to introduce their coins to its facebook users and its network.
Wit that, they can profit in crypto with their own, not by investing in existing coin, they want to compete with the existing ones but will not compete with bitcoin as they are launching a stable coin.