The real issue at hand here is that it’s difficult to impossible to discover why, or raise an effective appeal, when one runs afoul of Google, or suspects they have.
I shudder to use this word as I do think in some contexts it’s being overused, I think it’s the best word to use here though: the issue is really that Google is a Gatekeeper.
As the search engine with the largest global market share, whether or not Google has a commercial relationship with a site is irrelevant. Google has decided to let their product become a Utility. As a Utility, Google has a responsibility to provide effective tools and effective support for situations like this. Yes it will absolutely add cost for Google. It’s a cost of doing business as a Gatekeeper, as a Utility.
My second shudder in this comment - regulation is not always the answer. Maybe even it’s rarely the answer. But I do think when it comes to enterprises that have products that intentionally or unintentionally become Gatekeepers and/or Utilities, there should be a regulated mandate that they provide an acceptable level of support and access to the marketplaces they serve. The absence of that is what enables and causes this to perpetuate, and it will continue to do so until an entity with leverage over them can put them in check.