It's easier to travel via more environmentally friendly routes in Europe as opposed to North America due to its vastness. Bands the size of MA would also normally tour their our own PA which is practically another truck on the road which they won't require at festivals. It's generally more eco-friendly to hit a few festivals in Europe as opposed to doing a full tour (subject to routing)
Arena level bands with massive productions are huge carbon emitters. I've worked with Kiss and my god do they tour a hideous amount of stuff (multiple trucks, buses, pyrotechnics, private vehicles, aicraft etc) It's also going to be a hard catch-22 on artists, especially smaller acts, as touring really is currently the only viable way of generating sustainable income. Bands like Massive Attack can afford to take a few years off that would just cripple others. Ultimately they do still need/want to make money and I hope they and others continue to use their platforms to push for real change in a very wasteful industry.
Long-story short, - expect gig/festival tickets to continue to rise in price.
Enjoy your first Primavera should you chose to go! It's one of the most diverse and excellent festivals around.