My best guess:
1. The Astros don't expect to get Bregman. Getting Parades gets them a 3b who's tailor made for the Crawford boxes and an immediate replacement. They also get prospects (perhaps Warren, Smith, whatever). This gives them an immediate floor where they don't bottom out and can quickly get back to being good. They were into Parades at the deadline pretty heavily. So they get their second crack on him, and get prospects who could help shortly.
2. The Yankees probably sign Bregman out from under the Astros. They tried to get the Astros to engage on Tucker, maybe for Gil, maybe not, but once it became clear to the Astros that Bregman probably wasn't happening, and the Cubs offered Parades, they pivoted there. Bellinger gives you Dominguez cover if he doesn't hit, but can also handle 1b or a corner spot. Bellinger, a LHH, is a good fit for Yankee stadium.
But that's me just trying to see things from their perspective the best I can.