I think it's pretty easy... using Waterfall management methodologies. There's too much up front planning and not enough actual development. By the time coding actually starts, the business needs have changed.

True, but problems with "waterfall" go way beyond that.

It's not just that the business needs change - it's that many clients are simply unable to state all their business requirements and rules in one shot (even if that shot is done over weeks or even months). I sometimes find that client's rules are so 'patched' that a full-blown discovery process uncovers the fact that clients have been inconsistent in their own rules. So sometimes buiding a brand new system uncovers so many of these, that the system becomes a "proof of concept" for their rules. And that process sure as heck can't be neatly determined on some bean-counter's ledger! ;)