What went wrong with public procurement?

Once upon a time, the idea of well-run, non-corrupt RFPs and bids was an extraordinary achievement of the civil service (see Caro's description of NYC procurement in the 20s under Tammany Hall).

However, today, procurement, at least for things like software, is bureaucratic, slow and often limited to a small number of established players.

How did this happen? And does this tell us something about 20th century government vs the 21st century?