I have seen this as well.
My theory is that while the Kemper is aging, it still offers the best live interface of the available devices. I also think the Kemper has a reputation of pretty solid reliability in live environments that gives gigging musicians peace of mind. Updating the firmware on Kemper has no effect on the existing sounds you already have stored in performances and rigs. This provides stability in tone across the years you use it. Finally, I think there is the "I know someone else that gigs with it" going on a little too. It's been the #1 live digital amp, therefore it is most likely the pick of someone new moving to a digital amp for their setup.
I'll give it to you that Kemper is ugly. Looking at that glorious color LCD on the QC, you can't help but be envious as a Kemper player. Of course, there was nothing particularly "beautiful" with our old tube amps and cabs. Perhaps guitar players aren't the best judge of "beautiful"

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