Object oriented databases store binary objects as opposed to object-relational databases Mike pioneered with Postgres. The plan was for CORBA, common object request broker architecture, to shuffle versioned objects around the web and object oriented databases would store binary code objects.
Mike's answer? "Because the money is in transaction processing. Banks pay millions of dollars for transaciton systems. Transactions are the meat-and-potatoes of database sales."
In some sense database companies are wise for ignoring the web. Web companies are now hell bent on "move fast and break things." A transaction database is the antithesis of move fast and break. Transactions move deliberately with consistency. Durability says I can unplug my database at any time and bring it back up. This is the opposite mind set of move fast and break things.
Here in the valley whole QA departments are being disbanded in favor of LEAN and move fast and break things. All of this is antithetical to the database world of transaction processing.
At they say: you get what you pay for. What the enterprise companies are paying for is exactly what is being delivered. Open Source fits the every changing, move fast and break things of the web world.
To whit, you might see database vendors move into the web space some day if in fact companies are willing to pay millions of dollars for them.