»Zion Mainframe codes in M1«

In M1 Agents were obsessed with getting Zion Mainframe Access Codes.
They seem to need the codes to somehow destroy Zion (from inside Matrix?). But in M2 and M3 there is no mentioning of Zion Mainframe. Why Agents gave up the idea of blowing up Zion through Mainframe in M2 and M3?

As Morpheus explained in M2, "We have freed more minds in sixth months alone than in sixth years. This attack is an act of desperation," or something to that effect. There was no time to get the mainframe codes without risking losing more minds, apparently...or the Wachowskis just kind of thought this would be more visually entertaining. Whichever.

The reason we do not hear much about the Zion Mainframe is because M2 was mostly about rogue programs....

Which is what pisses me off about Revolutions. Smith should have been more than just Neo's opponent.