A coach of the class of Jose Mourinho needs the full support of club management to do what he wants without any restrictions, and if he doesn't get that then he won't stay long in the team. Of course for a coach this is important because he can apply existing strategies without being hampered by anything, that is very good for the progress of the team. But AS Roma itself is not that easy to let its coach move alone, they are still limited in certain respects. I understand this, maybe they are hampered by something they cannot do freely, such as the club's finances for example, or other factors.
Mourinho got great opportunities at Manchester United, but this did not lead to anything, so it may not always give the expected result. I think that he will receive some kind of funding, since for two seasons in a row he took Roma to the Euro Cup finals, but this funding would be much larger if Roma won the El final and got a place in the Champions League. By the way, Mourinho decided to stay at Roma, so apparently he still got some kind of budget to strengthen the team.