When did the owners balk? It was Vos and the Republicans in Madison that scuttled the initial $295 million proposal by Evers. They (Vos et. al.) claim they are 'still negotiating'...

The Stadium is 'owned' by the "Southeast Wisconsin Professional Baseball Park District" (a government entity), which is responsible for overseeing, operating, and maintaining American Family Field.
Under the existing terms of the current lease, the District is responsible for all repairs and maintenance, as well as upgrades to keep the stadium "on par" with the top 25% of MLB stadiums. Not sure how they measure that, but it's part of the contract.

The Governor's proposal, between the initial amount paid, interest collected on that amount, and other accounting magic, would have covered all Stadium District obligations (repairs, maintenance, and a number of upgrades to maintain that 'top 25% status' - not everything on the 'wish list' by any means, but enough to meet the terms of the lease) through 2043. The proposal also included a lease extension for that same length of time as well. It sounds like Vos wants more years (among other things).

The District was previously funded by the 5 County Sales Tax; once the initial construction costs were all paid off, they shifted the tax to go into a maintenance fund until it was sunset. It sounds to me like the amount in that fund would cover just repairs/normal maintenance for some length of time, but it would not fund any upgrading to maintain the 'top 25% status'. Which, at some point, if they fail to do so (or if the District should just run out of cash, which will happen eventually), the lease is automatically broken.

At that point, given Manfred's recent comments, I would assume MLB (who probably hates even having a team in Mil given the small market size) would jump on that opportunity to say "A-HA!!! YOU HAVE NO STADIUM!! TEAM MUST MOVE!!!!!"

I hope they can work it out...