If someone's been consistent for months or years, doing something different can improve their performance. We know that people who strength train will run better and get injured less often, but it's also true that people with better cardiovascular fitness have fewer injuries in strength training.
If I had my ideal way for my gym, I'd set it up like university. You'd do 12 week terms with a rest week after each. 3 terms would be basic barbell stuff, then the fourth term would be something different. If you were powerlifting (squat, bench, deadlift), you now do weightlifting (snatch, clean & jerk). Or you run. Or do kettlebells. Or play tennis. Whatever. And of course vice versa, the soccer player who spends 12 weeks a year just lifting is going to do themselves some good. You then return to your primary interest better at it, and feeling fresh and still keen on it - rather then grinding away and getting sick of it.
The other thing is that most people who get injured and return to their primary interest actually end up better at it. That's because the injury makes them stop, which gives them a rest to recover other non-injured parts too, but also to reassess what's helping them and what's not.
Whether with formal breaks and changes put in, or forced in because of injury, you return to your primary interest with some insights from the other one.
The same of course applies to gaming. If for example you normally play D&D and then spend a few months playing Traveller, you come back to D&D with some insights, and play D&D better.