Why isn't the V flight formation being used for commercial purposes?
This possibility has actually been studied and discussed (e.g. here, here, here) as a way to save fuel costs, but there are several issues with implementing it today:


You need to schedule a number of aircraft all flying the same route at the same time for a significant amount of time
If different, competing airlines should participate in one formation then they have to cooperate and be satisfied that no one is at a commercial (dis)advantage
A lot of work would need to be done on procedures and training (how does the formation form up, who takes the lead, how/when does the formation leader change, how are emergencies handled, what flight levels are used, what separation is required between formation and non-formation flights etc.)
Autopilots, software and other equipment would need major updates, which in turn requires re-certification
All relevant regulations on separation, formation flying and so on would need to be reviewed and changed which in most countries means changing the aviation laws, and changing any law is usually a long, slow process


Having said all that, you'll notice that most of those issues are procedural, not technical. In theory it's a viable approach, but turning that theory into reality would require a lot of work.