I'm going to try and write this carefully because it could easily offend, but this is the way I see it: as someone else said, Marcus Rashford is a marmite player and there are a number of reasons for this, but mainly it is because his famousness transcends his footballing ability.
A nephew of mine is just getting into football and his family are longtime Man United supporters..... During a game on TV recently (and a family visit) he asked me if Rashford was playing, I said he was, he told me Rashford was his favourite player, I didn't say anything. He watched the game for like 1 minute, spotted Rashford and then he was off to play Mario Football on his Nintendo. So why does he think Rashford is so great? Well in his school are tons of books with Rashford's name on (he doesn't write them alone, but co-authors with someone else, and the authors name is in a much smaller font) but Primary teachers are desperate to get kids reading and especially lads, so they just order boxes and boxes of them. He isn't quite David Walliams, but he is doing Ok. Rashford is not so much a footballer now, he's just got incredibly famous. This is the main reason why Man United won't initiate a sale - a bit like with Ronaldo - he is a valuable asset to the business way beyond what he does on the pitch. You have to admire the guy and indeed his support network (family/agents) who have monetised the Rashford 'brand' so successfully. One of his recent books is called: 'You are a Champion: How to be the Best You Can Be' and c'mon that is taking the mickey. He often doesn't try 100% in his job and that has got to be Chapter One, Page One of any self-help/advice guide and when United were last Champions, he will have been 15 years old.