https://en.wikipedia.org/wiki/Trademark_dilutionThey're basically trying to monopolize a commonplace word in a way that prevents others from ever using it in any combination.
It is exactly as silly as Apple suing a fruit store that sells apples for having a reference to apples in their store name.
If you don't file (petty) lawsuits like that one, you are liable to lose the trademark, because an opponent may argue you're not defending it. "Bing" is an onomatopoeia, and "Yahoo" is a shout (and also a kind of bird, and a colloquialism for "big dumb brute"), to name a few examples, and they have been trademarked by the business ventures of the same name. So yes, a commonplace word or expression can be trademarked. There are a lot of people with the last name McDonald out there, but if one of them named his business "McDonald's", there would be trouble. That's how it goes.