The purpose of a trademark is increasing trust and reducing fraud. E.g., when I buy lithium batteries I intend to store inside my home there's only so much I can do to audit the internals, so I rely on brand recognition to help purchase safer options. Other people and brands are welcome to sell lithium batteries, but masquerading as the brand I'm attempting to purchase from is damaging to that brand and to myself.

When other people use your trademark (even legitimately, as the courts have deemed for TFA), it's possible for that brand you've built to slowly morph into something other than just a name for your business or product. Band-aids and kleenexes are some classic examples, and the phrase "super mario" referring to more and more non-Nintendo things over time could do the trick too.

As something of a side tangent, this is philosophically related to the "heap" problem -- if you place one grain of sand at a time in a ___location, when does it transition from being an assortment of grains of sand into being a heap of sand? Which grain makes that transition? In much the same way, which trademark infringement dilutes the brand enough that when a court tries to go back to first principles they'll finally side with the infringer because the public doesn't actually recognize your brand name as referring to you in particular sufficiently often?

The playbook they're exercising is keeping that philosophical collection of sand very small. There isn't any legal recourse for suing a thousand infringers once public perception has shifted. Growing your brand and reducing the flow of sand to a trickle are both allowed though, and the legal half of that is the latter.

Note that the playbook says nothing about whether those are legitimate uses of your trademark. The thing you're fighting against is changing public perception, and you're trying to slow the change down as much as possible, using the courts as a cudgel.