I think one of the major driving factors initially was that Ubuntu didn't follow the long package tree freezes that Debian stable/testing was subjected to after

I think one of the major driving factors initially was that Ubuntu didn't follow the long package tree freezes that Debian stable/testing was subjected to after a period of time. Debian stable still tends to contain older packages with security patches applied rather than the latest and greatest(tm), which most standard users tend to prefer over stability