Ask HN: Why Google Voice doesnt give out listed vanity numbers?

hi everyone, I wanted to ask if anyone could explain why Google Voice does not let me take vanity numbers even if they appear in search results. The ones I tried to get are as following and Google Voice says "We had an error. Please try later"

(424) 999 8809

(424) 222 9399

(424) 244 0045

(707) 515 0555

(707) 400 0707

(707) 200 1214

(313) 444 5444