Most of the software we use hasn't existed long enough for real specialization. Hell, there are still people who were alive before software existed.

If you ask me, the real problem was whatever legal technicalities allowed vendors to create certification programs for "experts" using their own software.

Most likely this. When you have a horizontally sharded MySQL database that spans multiple datacenters - managing replication, failover and scaling out is not something you would expect most developers to be able to handle.

Let alone fine-tuning various kernel parameters, in depth monitoring and other performance tunings.

EDIT: Sure most experienced developers would have a high level and abstract idea about various things that may be outta whack - but it takes some one with expertise in the field to go beyond guesses.

Managing databases is an operational overhead. You want to minimize expenditure on it. Developers create IP. You want to maximize investment into that.