[Symmetry]

Just because a word is trademarked doesn't mean that someone else can't use, or even trademark, the same word in a different line of business. I can't call my new OS "Windows". I probably won't be able to start a line of computer monitors called "Windows" either. But if I wanted to open a line of restaurants under the "Windows" brand I'd probably be fine. Trademarks are only enforceable when there's a danger of consumer confusion.

[mint2]

In theory yes, but when a litigious company has deeper pockets, being in the right doesn’t matter if one doesn’t have enough money to prove it.

Barring that type of one common word trademark would prevent some of those or make it cheaper to defend.

For instance backcountry online suing things like coffee shops called backcountry nitro coffee; outdoor safety clinics called backcountry babes that taught avalanche safety for women; and many more.

One word Generic terms in any field should explicitly not be trade-marketable.