CG won't do it because they can't figure out how to monetize it. Just like they won't do any other sandbox options. It would be a waste of their time, money, and resources and not enough of our money, time, and resources.
Even though, other similar collector games have friendly match options that work great, CG doesn't want to pay attention to that because they think they know better than decision makers for other games that are making more money than SWGOH. Instead of whoever is running CG acknowledging they're wrong, they'd rather just keep making new things that suck.