I was trying to keep the politics out of it but anyway, so here is my 2c.
There’s no way the company was going to let us continue checkerboard. What I heard (hearsay alert) is management was so upset about how we (ab-)used the rules they agreed to, they were going to make sure abuse was impossible. I don’t think the NC gave up voluntarily. 75% of us, including me, voted yes, because we thought it was good/good enough/the best we can get with this management & NC & NMB/needed money for a boat.

The reserve rules were definitely gutted to a far bigger extent than required for coverage protection. Being able to drop days from the outside in provided the grid is (very) green would save the company money without danger of scheduling disruption, but is no longer allowed so was done IMHO for purely punitive purposes.

This might not be the only reason, but upgrade has gone from 54% RS before contract to 63% RS (from latest what-if). Could be the higher pay rates or PBS, but I think lots of people bypass because reserve QOL.