The Brewers are in baseball purgatory, not dissimiliar to where the Sox were just before they began the rebuild. A weak farm system and an MLB roster of stars and scrubs, their stars being Woodruff, Burnes, Hader, Williams, Yelich, and maybe Hiura. They can conceivably compete in and maybe win a weak NL central, but no way are they contenders in the NL with the likes of the Dodgers, Padres, Braves, and Mets. And they don't seem to have any appetite to add to payroll in the current environment. So they can keep all those guys above and be a .500ish team with them for the next 4 years, or look to trade them at peak values to try to add elite talent to the farm.
For those that don't think Madrigal would interest the Brewers, I disagree. Madrigal is exactly the type of profile the Brewers covet (good avg, good walk rate, low strikeouts). Stearns even said as much when they acquired Yelich (back when his career high in hrs was only about 18) and Cain. Hiura is no obstacle to any Madrigal interest. The universal DH is coming soon and that's where Hiura is going. If there's no DH in the NL this year, I'm sure the Brewers would be willing to move Hiura to 1B for the season.
What I don't understand is why the Sox seem eager to part with Madrigal and Heuer, or why the Brewers would want current MLB players. A package of Milb players (Steiver, Kelley, +) makes more sense to me.