I was working for Slicehost at the time, we were a tiny team working our butts off in a loft office in downtown St. Louis, with a few remote employees.
To my understanding there was a runway-growth problem. Could the founders raise and spend (efficiently) enough money quickly enough to keep the business viable? It would be a big gamble and the alternatives were to shut down (no way!) or sell. So they sold.
Rackspace wanted to take Matt’s and Jason’s know how (plus customer base) and go big, really big! That defocused our efforts a bit, plus there were corporate integration headaches (though not too bad). Eventually Linode, already a competitor, and later Digital Ocean filled the void.
All I can say is thank you. I learned to manage servers because of Slicehost and the articles on it back then.
I remember being excited by the merger because well, Rackspace had such a fantastic reputation at the time. People still tell stories about their service. The Rackspace Cloud was just up against an absolute monster in AWS and never really became competitive.