Real life answer is money! Clients make purchasing decisions based on many factors but usually most important is the budget; not potential value of investment over 10-20years-lifetime of the system. Due to this simple fact, oftentimes analog products are the only reasonable solutions that fit clients' needs. If there was minimal or no competition in the marketplace, an installer of course could influence an uninformed client to spend more than initial budget allows. But again in the real world, with lots of competition (especially now-a-days with so many cheap china made products) and many clients requiring video surveillance to be only "good enough" image quality, analog is the only answer TODAY!
In the future, analog in the marketplace will go the way most analog products of yore... ie analog cable tv.
The day low end ip solutions and products will offer the same quality and price, that's the day analog is gone. For now analog is the only realistic option for many, many projects (for ex: almost all landlords of apt building here in nyc go with analog).
For clients with budgets that allow for ip solutions, ip components are the obvious choice.