Why? I don't understand this. Mozilla needs to make money somehow. Unfortunately we don't live in a post scarcity world where programmers just contribute to OSS because they enjoy it and want to make the world better. Currently they do it because of those things AND because they need an income. Unfortunately things still cost money. (I think this answers your last few questions as well too)
> If it is so unpopular, how come Firefox hasn’t axed it?
I think this is sampling and internal bias. Have you seen the numbers of clicks? I haven't. But I rather like pocket.