Why would they clear out djvu? It's one of the best/most efficient storage format for scanned books.
It's not just about laziness preventing one from installing the more obscure ebook readers which support djvu. It's about security: I only trust PDFs when I create them myself with TeX or similar, otherwise I need to use the Chromium PDF reader to be (relatively) safe. I don't trust the readers that support Djvu to be robust enough against maliciously malformed djvu files, as I'm guessing the readers are implemented in some ancient dialect of C or C++ and I doubt they're getting much if any scrutiny in the way of security.
And since you're creating the PDF yourself seems like you can trust it? Since nothing malicious could survive the DJVU to PDF conversion since it's just "dumb" bitmap-based.
If your DjVu file contains an exploit for your DjVu decoder, even if you run it in a bombproof container, it could still conceivably inject malicious code into the resulting PDF file. That sounds far-fetched because the exploit payload would need to recognize that a PDF conversion was going on and respond by generating the PDF, but I remember when people thought exploiting buffer overflows was implausible, and this is not the same level of rocket science.
Evince doesn't come by default with Archlinux (my desktop distribution of choice), but I still install it everywhere.
This doesn't make sense; nothing comes "by default" on Arch, but evince is in the official repos as far as I see.
Yes, evince is in the official repos. Just like Chromium and Firefox. Or bash, but not any other shell (as far as I can tell).
As a format for preserving full native scan views (large, but often strongly preferable for visually-significant works or preserving original typesetting / typography), DJVU is highly useful.
I do wish that it were more widely supported by both toolchains and readers. That will come in time, I suspect.