I feel yahoo still does not understand how the internet works.
1. When yahoo buys things they die very quickly (Anyone remember geocities in the mid 90's?) Yahoo bought it and it died instantly.
2. Things like Tumblr have a relatively short lifespan people move on from things like that very quickly, Its nothing ground breaking and just something hipsters like in reality. Its been up for awhile and people are going to start getting bored with it if they already have not.