Maybe he does want to go. As Troy said, WC winner, world class, 27 now and attracting attention from teams that are challenging for major titles.
He came here to win those titles, but if we're not providing a team for, not only Pogba, but the other top class players we have, to challenge on all fronts, then eventually they will want to leave too.
That said, with the purchase of Bruno and other potential targets lined up in the summer, Pogba may actually think it's a team that could start challenging.
He's under contract, so the club will ultimately have the final say, but if he wants to go, as you said, we should let him and reinvest.