I don't know if you have been lurking around the forum before you got an account, but if you have been looking at the Ronaldo thread many years back, you would notice the amount of vitriol that some posters have for Real Madrid's year on year attempt to poach/sign Ronaldo.
Pogba was more of a mixed case - we recognised that there were a combination of factors that result in him leaving - there are quite a no. of debate, till now even, about how Sir Alex is the major cause of it by playing Rafael in CM against Blackburn rather than giving Pogba a chance. There were rumours of the Pogba and his agent demanding huge money, which is outrageous for a player from the youth who hasn't proven himself at top level yet; and Sir Alex isn't keen to set a precedence by giving in. Pogba's agent Riola is also quite well know to be a dick who constantly moves his players for money; Pogba himself is also quite the mercenary.