Someone said this ages before me but the page was meant to get Alan at the arcade, Alan inside the grid. Clu wanted him but settled for Sam. I want to dive a bit deeper into that, especially after reading betrayal (really the novel does wonder for his character and providing additional context for legacy).
Backup plan—
Contacting Alan was the last desperate attempt to find a normal way out. I can imagine Kevin would have talked about him quite frequently, about how good he was and maybe even admitting to clu he was the one to originally write tron. So, clu figures out a way to contact this “great user” and make him fix everything. Maybe he could finally give the grid a purpose from the outside or do some work on the inside to stabilize everything. I don’t even think clu knows what all needs to be done to fix everything- he’s been lost and a bit power hunger for a while now I’d imagine he’d be forceful with Alan but have good reason to be.
I think having Alan rewrite and fix the grid from the outside (or in if possible) would make the most sense. What the hell use would alan have otherwise? He wouldn’t have a disk! Sam only got one once he was put into the games, additionally alan wouldn’t have the knowledge of the grid to use his disk as a key after receiving one. So getting Alan in the first place had nothing to do with “out there” or “world domination”.
Last resort—
I saw a theory a while ago which I wholeheartedly believe that said, Clu only did all of this (the army, the world domination plans) to give the grid a purpose. It really makes his authoritarian decent into madness all the more tragic, as stated before he never had a chance to be good. He can’t create new programs he can only rewrite what’s there— he’s slipping and out of ideas because endlessly building in a overheating system is a absolute nightmare. A mindless army works great as it takes up as little energy as possible, you can conserve what remains and give your citizens something to actually do… now mind you it’s not a good something to be a mindless drone. After Alan falls through he goes on with the first plan. I also believe the world domination thing also comes about because he’s a reflection of Flynn’s  arrogance back when he made the grid— this is so his speech can almost identically match Flynn’s “in their is our destiny!” -> “out there is our destiny!”. More that for a character motivation that makes sense.
Clu is a dangerous line. As the more you read into things the more sympathetic he becomes the more you understand his motivations and what lead him down this path. You almost forget how horrible his actions are from how badly a hand he has been dealt. He is fascinating and so unbelievably sad that he saw this (Dictatorship, mind control, genocide ,etc.) as the only way out. He is the antagonist but not the villain.
Sam—
No one was expecting Sam to be the one to arrive at the arcade. Clu didn’t take Into account Alan’s care for him,  probably because clu had his own issues with Sam since he was a baby. It’s interesting as Sam is basically the crux that sets off the film. Plan B didn’t work so we’re going for the crazy world domination plan, let’s use you to lure your dad out of hiding. To me it sort of comes through as the backup plans of backup plans to him- if Alan had come would he have concerned himself with Flynn at all? This god is helpful, this god sticks to his words and thinks things through…oh god the absolute angst potential in that. (Again keep in mind that Clus hatred is for a Flynn who didn’t go through 20 years of  philosophy lessons).
This is all me just theorizing anyway, my own way at picking through legacy trying to understand it. 🤷♀️ Clu is such a fascinating character that you really have to feel bad for, and again it’s a little concerning? Because you forget how much bad stuff he really did just because they fumbled Flynn SO hard. The Kevin Flynn who made the grid does not feel like the same Kevin Flynn who broke into ENCOM with his buddies one night and I don’t know how to explain it.
…..I need to write an AU where Alan finds the Grid. He doesn’t even have to go on it - just him and Clu, chatting via a text box or something, fixing the Grid one conversation and/or diagnostic at a time.
Flynn: I’m making the perfect system
Alan: you fucked up a perfectly good system administrator is what you did, look at it! It’s got anxiety!
