Why use TCP? Video conferencing, VOIP, and other low-latency applications typically don't need guaranteed delivery. With the right error-correction, some packets can be dropped without issue, and an occasional cut-out is more acceptable than constant low throughput. UDP makes a lot more sense in those cases.

UDP has issues of course. Breaking through NAT is tricky, and you have a smaller selection of libraries and tools. Still, that trade-off seems a lot better than trying to get everyone to change their congestion algorithms and adopt new standards.