Because that's what he thinks is best for him. Lets be honest.
Ten Hag underestimated the league. He quickly adapted and overseen a decent season. What got him sacked was spending the next 18 months persevering with a brand of football that was never going to work.
Ten Hag already did that but fecked it up. By the way Ralfs original quote was referring to 8-10 new players. Erik went way past that.
I think there's a subtle difference. Amorim is sticking to his principles because he believes that ultimately this is for the best for himself but also the club.
It always struck me that EtH was desperate to save his own skin and talk up the job he was doing. He abandoned "his" football in favour of face-saving results, he consistently fed us claptrap about how well we had played when we could see how dour it was and he made excuses about injuries and refereeing decisions all the time.
The point is, you or I could walk into Manchester United tomorrow, set-up in a 4-2-3-1 middle block and go through the same old tired motions, and results would be generally OK. We saw that with RvN. Amorim could have done that and soaked up the good PR, but he's chosen the hardest path because he believes its for our long term benefit.
In terms of "open heart surgery", that doesn't just mean "new players", every manager wants expensive new players - it means removing the baggage and the wasters, even if that causes short term pain.
Rashford is a prime example. EtH indulged him time and time again because he felt he needed him. He's credited for taking on Ronaldo, but Ronaldo was completely and utterly shot in that final season. He was so far off the pace it was clear he was finished. Likewise, EtH indulged Sancho many times - it was only the public criticism that saw him dropped.
I could go on...the relentless malingering of "injured" players enjoying a nice jolly, the fact Casemiro should have never stepped foot on the pitch for United again after that Panenka vs Coventry, and then again after Palace, and then again after Liverpool...but EtH kept going back to him because he felt he needed him...
EtH was tough when it suited him or when he was personally insulted, but he pandered to the players he felt were useful and allowed them to get away with murder.
No such messing around with Amorim. We have seen Rashford taking the absolute piss out of the club for three or four seasons...he lasts two or three games under Amorim and never plays again, despite Amorim acknowledging that on form, he's our best attacker. Casemiro has barely had a minute since the Newcastle debacle. A warning shot was fired at Garnacho...and look how his form has improved.