I think since about 4 years back, a worrying culture started to develop where our players basically diverged into two groups, the talented players on the ball who didn't do much work off it, and the grafters off the ball who weren't as talented on the ball.
It almost seemed like if you were skillful on the ball, you didn't need to work hard off it, and for the others, if you worked hard, it was Ok to be average on the ball.
The games of Rashford, Shaw, Martial, Pogba, Greenwood games were formed through that I feel (Sancho joined it), and it's an adjustment to shift that mentality. The types who will just stop and glare at the ref if someone is tugging their shirt, or glare at a teammate if the pass is not exactly where they want it.
On the other hand we had the likes of Fred, AWB, McTom, Elanga, Dan James who went hard into tackling at least, even if some could still be guilty of jogging when we've needed to recover and get back (McTom and AWB).
It's clear that to be a successful team, players need to be good on and off the ball, and for the likes of Rashford, it doesn't come naturally, so he's needing to very intentionally adjust.