Because they are hoping that by focusing on one aspect of the system, they can protect the core of the system. If you spent a decade gaining complete control of elections and saw that it could all be exposed, would you let that happen, OR would you insert your people in the "right" side to direct the focus to smaller aspects of the system, like Dominion, a single technician, even Zuckerberg private funding, that can be "sacrificed" at little inconvenience (and possible gain, e.g. you would now supply new "non corrupt" voting machines) while maintaining the core system? You would do the latter - and I suspect (and have evidence that supports) that's exactly what's happening.