So if you got malware the last 20 years your system could still be infected? Not saying that risk outweighs the pros, but that is something I think is nice each fresh install.
It is good to run this once a while even for non-security reasons: you can detect hardware problems (notoriously failing SD cards in Raspberry Pis) and mistakes, like installing a custom program to /usr instead of /opt and accidentally overwriting system files.
(Granted, those are unlikely to survive for many years without breaking or otherwise getting caught)
Yeah, backdooring configuration/bashrc is a problem, unfortunately, you will probably copy the configuration after the reinstall, thus copying the backdoor too.