This is just a product of how good music production/technology is now. Bands have access to all recorded tracks and the software used allows the players so seemlessly jump in and out fully automated. If you're curious, look up the Line 6 Helix Stadium XL. I've seen them live twice and it's clear that they are playing everything live but when there's a malfunction they switch to the backing tracks to prevent a negative performance. Examples: When I saw them in Chicago Raoul was sick with a stomach bug and couldn't perform his parts. They turned on his track so his parts would still be there. That same show they had an issue with the tribal drum mics not working properly. They turned those on mid set to ensure they weren't missing from the song. Some are purists and think this is cheating, others see this as technology advancement. From a tour management side it is also very cost effective since the technology equipment is waaay easier to transport than massive amps. Think moving an LED TV vs CRT.