Because P2P is terrible for audio and video? The quality of call I'd get on skype would be random because you never know if the system will route you through some kid's oversaturated DSL line or 1gbs fiber.

On top of it, p2p apps like the old skype and spotify aren't very nice. I've seen them make 3-5mbps DSL borderline unusable. This is unacceptable in a business setting and home users may not be aware that they are hitting a cap with their ISP when running these apps.