Has something to do with legal precedent and a desire to keep tight control on their brand. Basically the more you let other people "use" your brand in a space without any control or input from you, the less ability you have in court to enforce a cease and desist if someone eventually uses your brand in a way you don't approve of. (or that you fear could be damaging to you)
I'm not saying I endorse this status quo, btw, just that this is the big picture reason for individual seemingly petty cease and desist letters. It's rarely about the micro-infringement itself and more not wanting to cede even a tiny measure of control.
(Now multinational corporations and their obsession with cultural control in general, that's arguably an even bigger problem that this sort of thing is more a symptom of)
Oh yeah, what were we talking about?
Something about how to turn someone into the perfect girlfriend within a year. Don't let corporations know about that one.