This is true today, but 3-4 years ago Spaces was actually a completely separate product that was so bad that most Googlers didn't even know it existed.
I have never met a single person, including on the Spaces team, that used Spaces for anything. Ever.
Consider Google+ also. They had plenty of reference points for that. It was just not very good.
Google tends to abandon development on new projects way too quickly, before they're ready for mass appeal. They probably expect it to explode like Gmail did. But I think they forget they lost a lot of promotors like us when they abandoned the don't be evil thing.
At the time I recommended Gmail to everyone, now I try to get people away from Google :)
"We couldn't figure out how to market it" was from an interview straight from the people who made it: The companies they pitched to responded with things like "why would we need this, we have email".
The first part of it is not true (but the second part is true, in that you can access chats from Gmail as well).
I just checked, and Google Chat exists as a separate app on iOS, Android, and web (chat.google.com). Even though the web version redirects to a gmail url (mail.google.com/chat), it is still a separate web version, not embedded into gmail. The only thing it shares with gmail is its subdomain, the page itself has zero mention of gmail or any gmail-related functionality.
I used to have this app installed, then one day it started telling me I had to use the GMail app for chat instead.
I wouldn't be surprised to hear that they were rolling the out the migration to accounts incrementally, or they've reversed course. But I deleted the google chat app because it wouldn't let me use google chat.