Inside publishing offices, people who give a lot of blurbs for books are known as "quote whores." It's very much a game of who you know, who your editor knows, who your agent knows, etc. It's not to say a blurb is worthless, but a blurb from someone who doesn't give a lot of them may be worth more.
Editors do try to get and use _relevant_ blurbers. And a weak blurb probably wouldn't get used unless they really had nothing else. Also, the first readers of blurbs are booksellers and reviewers, not readers, who may pass over a title if no one is willing to vouch for it. If you present a title to your sales team with no blurbs, they will make frowny faces at you.