For me there are a few reasons I am still a Bryce user.  I have an enormous investment in Bryce content, some can be ported to other rendering software, most would be lost if I ceased to use Bryce. I no longer have the time to learn another app as I am now an occasional Bryce dabbler rather than a regular user. I paid for and have the Bryce 7 Pro software, and have concocted a way to continue to use the app even though it will not run on current Mac operating systems.

That said, if somebody told me another app was there that could use most of my Bryce content, that was reasonably easy to migrate to in terms of learning to use it, and would run bug free on current operating systems, and be affordable (say under $300) then I might be tempted...