Product design and product management is bad. Many of the software products are given resources beyond their needs, while others are slowly starved. OCLC's nonprofit status encourages this, as the bottom-line costs and benefits of any product or project are often not given enough consideration.
While the technical staff has above average competence, the demands of some product managers go so far beyond what is necessary or useful that the software developers and systems administrators find themselves overworked and far outside their areas of expertise. This leads to poorly implemented software and systems, resulting in more overwork.
The field of library automation was an early adopter of computers and the Internet, so there is a strong contingent of older software and data that one must navigate at OCLC. (I didn't write "legacy" software and data because there is no indication that any of it is going away soon.)