Maybe United realise that their level of competition is Newcastle and so are trying to snatch Sesko away from them? 
But I don't know why he should choose them over Newcastle.
In general, against the backdrop of other teams strengthening their squads, United still looks like they are lagging behind. There is still time before the end of the transfer period, so let's hope for at least some positive news, I can't stand another season of "we have to wait for next season" from United.
Manchester United are team with commitment, whenever they want, they will get it even though they spent more than what it should be. Newcastle is actually a rich team, but they're so careful to make a bid, it's like they don't care at all with Sesko. But I don't know why he should choose them over Newcastle.In general, against the backdrop of other teams strengthening their squads, United still looks like they are lagging behind. There is still time before the end of the transfer period, so let's hope for at least some positive news, I can't stand another season of "we have to wait for next season" from United.
The reason why Sesko choose Manchester United over Newcastle because he know joining Manchester United will make his follower reach 1 Million and it's easier to make the fans happy.
If he join Newcastle, people expect he should be as good as Isak. If he join Manchester United, all of the strikers are trash.
United are still a big brand now but they are no longer a team you can go to and expect guaranteed titles. How are they better (at the moment) than Newcastle which will be playing in the Champions League (where every ambitious striker wants to prove himself)? Only money, and it seems United were able to offer enough for this (82.5 + 2.5 million in bonuses). I don’t know how justified such a price is at all, for example, if Newcastle bought him (which were ready to give 80 million), then even if they sold Isak, they would not be in the black that much. However, the contract has not been signed yet, maybe everything will change.