Why not make DB2 do what Oracle does well?
There are some key features that make Oracle attractive to an enterprise that DB2 just doesn't do. Why didn't IBM try to add those features to DB2 and then the IBM shops might choose DB2 over Oracle?
For example, Oracle has an active-active shared everything environment in Real Application Clusters (RAC). That makes it very attractive. DB2 HADR is a shared nothing, essentially active-passive solution. However, a little product called Gridscale can make DB2 work in an active-active manner like RAC so why don't IBM buy it and resell it? They talk about it in their magazines!
Oracle partitioning is another key feature that can be mapped quite easily to existing DB2 functionality, and although IBM claim they can match it, is it really there when used at scale?