It's not as simplistic as this, though.
I've stayed out of the will he stay/won't he stay debate thus far (because I'm mostly just happy to wait and see rather than speculating) but it's not a case of us being more tempting than you. If Pochettino was unemployed and could choose either job, of course he would pick Manchester United. You're a far bigger club, with more resources and an incredible history. There's no doubting this and I don't think many of our sane fans would think that we can compete against you for players or managers in a straight fight.
The situation here is different though. Pochettino has invested years in to the club and we're about to move in to an incredible new stadium (Alright, it's just a stadium but it does have the feel of representing a new era for the club) and you have to feel that Pochettino will want to complete his project. He's already settled here, with a long contract, and is worshipped by the fans. That's a difficult position for anybody to leave, he would be walking away from a position where he's very comfortable before even seeing the job through.
Alright, so on the outside United are an incredible opportunity. Big name, big money to spend. You're also a tremendous risk which has killed the careers and reputations of 3 managers in a row. With your name comes the weight of expectations beyond the ability of your playing squad, fans who both want free flowing football but also seem to demand trophies because 'we're Manchester United' without understanding that means little when teams have stopped fearing you.
There's talent in your team, but I also see players who simply will not function under Pochettino and will be difficult to move on from the club because you've already handed them insane contracts. You have some that I think Pochettino could work with (Herrera, Martial, Rashford, Lindelof etc) but also a lot of players who are past their prime and won't work in a high pressing system. Players signed by Pochettino quite often take a season or so to adapt to his demands (Son being the best example) so even though you have money, it's going to take multiple windows until you get a team which fits his vision. In that time it's perfectly possible you could miss out on Europe again, go on a trophy doubt .. even not play particularly amazing football, we certainly didn't in his first season at the club.
Problem is, the media will be all over him like a rash in that scenario. Pochettino knows this, he knows he won't get time to apply his long term vision at the club if he fails in the short term. You aren't the same Manchester United who gave Ferguson time, you're like every other cash rich club. That's a hell of a risk for him to take considering he's still a young manager, working in London for a top 4 club where he's loved and has invested time. He's an intelligent man who will have considered all these factors, and I have no doubts that he's attracted to the idea of resurrecting a fallen giant and working with the biggest club in the country. To say otherwise would be delusional, but it would also be delusional to suggest he'll run to United without a thought, we're talking about an intelligent man who will no doubt be weighing up the pros and cons of moving.