I didn’t watch more than the first few kicks, so I could’ve missed some explanation afterwards about why it’s done this way.
We didn’t always do them like this at my previous school, but my teacher had us do this somewhat regularly. His reasoning was it’s teach proper follow through with the kick. Rather than just kicking out and back, drive through the target. Obviously if you hit someone hard enough with it you’re not going to complete the spin. It’s also equally important to strike and pull back afterwards so you don’t leave yourself vulnerable.
And the 360 spin works on balance, coordination and agility. It’s a good thing to practice. People bash the jumping and spinning kicks often seen in TKD. While I don’t think they’re very practical in an actual fight, they’re great for training. Burpees, push-ups and the like have no direct fighting application, yet no one in their right mind says they should be avoided because they’re not fighting moves.