These companies spend a great deal of time and money attempting to develop such software. Regrettably, they cannot spread the development cost over many applications, so it costs them more to develop and maintain this software than it would to just buy the PushAp Kit, now that it exists. In addition, creating data distribution software from scratch is generally not the company's primary competency, so the resulting software is often complex and buggy. Each directory service center runs a pushcache to cache local copies of directory files. Adding new service centers is easy - one merely places a pushcache at the new office.
Updates are efficient, and the pushcache handles the geographic distribution easily.
The development time and cost have been greatly reduced, and the result is better.