Not just a network provider preference. It is an OS-level preference in most consumer hardware today. (The "Happy Eyeballs" protocol, among other things. OSes will send IPv6 first, then after a delay send IPv4 and after that favor whichever one is "quickest"/"healthiest".) It's also a natural preference over things like STUN/"UPnP" to avoid NATs, especially CGNATs.