Their initial success may not have been, but their sustaining success absolutely must be, or else it would have fizzled out, one way or another. Many celebrities tried to latch on to this style of success as their careers waned more generally, (Jessica Simpson comes to mind, she had a similar enough reality TV show and was a big star for her time), but there was no sustaining power there. Not saying she isn't in her own right successful (she is), but by all given metrics I can think of, the Kardashians are outliers here

How about these examples? Amiga had customers, and was profitable, yet Amiga is no longer a force in the computing, nor is Commodore.

Both had more (arguably) capable operating systems than Windows (until at least Windows 95), yet, no sustaining power.

Look at the sustaining power of iOS and Android, despite other more capable competitors that tried to win market share (Windows Phone, WebOS, and I really wanted WebOS to win, mind you)