If a company does not make a consistent best-faith effort to defend its trademark(s), the claim on those trademark(s) get severely weakened. Companies are thus legally incentivized to defend their trademark (at least in the U.S.). This is a rational decision that has nothing to do with being an asshole (or not). If a company does not have a consistent track record of defending its trademark(s), then their claim gets severely weakened from a legal standpoint. Period, end of story.
And yet, every month there is a story like this in the news of "big company with generic name sues small company with same name" because nobody likes a bully. The problem is, if they DO NOT attack, the trademark claim will become severely diluted and then THEY will become vulnerable to a trademark dispute from someone else down the line, and the other party will point to their lack of historical defense and make an argument that the claim on the trademark is weak.
You're only incentivized not to unreasonably postpone a legal claim. Here, the company seems to exaggerate what a reasonable claim is in the first place.
And yet, every month there is a story like this in the news of "big company with generic name sues small company with same name" because nobody likes a bully. The problem is, if they DO NOT attack, the trademark claim will become severely diluted and then THEY will become vulnerable to a trademark dispute from someone else down the line, and the other party will point to their lack of historical defense and make an argument that the claim on the trademark is weak.