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.
Well to be fair here Mourinho did win the Europa League with Manchester United, but I agree that he wasn't that successful overall given that he had quite a lot of resources at his disposal. But his success rate in the various cups has been on a decline for quite a while now. He won a lot more titles during his earlier career. I don't know whether he changed or whether he just got a little less lucky over time. The fact that he won all his finals except for one (now against Sevilla) is quite an impressive statistic. At Roma he knew hew couldn't expect to buy players that cost three figures, but he gave it a try regardless. Everyone is now looking forward to his decision about his next step, but my guess would be PSG.