Tcp packets require syn/ack, which makes them work quite poorly on wireless networks where devices are receiving the majority of packets. What happens is now your tcp acks go through the roof, because sending that packet from devices may not be received.

But syn/ack is only for data you want to make sure was received. Things like video and audio don't need that to view the content.

So it's one big use is it's a protocol that works over wireless much better for content viewing.

You can test this yourself with a basic server and a mobile phone over WiFi at distance. Over http/2 video will cut out and have a difficult time loading. Over quic it'll just keep going.