google play store - Why do some devices ship without the Market installed?

Someone explain to me why some tablet manufacturers use software hubs other than Market. I bought a Coby Kyros ($160 @ KMart, Puerto Rico) and it brings AppsLib instead, and I immediately noticed that not all apps are there. I already found steps to root the tablet and install Market, but the question still bugs me.

Answer

Google only allows the Market, which is not open-source like the rest of Android, to be bundled with devices that passes their Compatibility Test Suite. Devices that do not pass are not "officially" Android devices.