It would be helpful if this could be applied before new releases are deployed.
As Limesurvey is a open source software, testing depends mainly on its users (like you and me). Before a new version of LS comes out, there are usually Alpha Releases, then Beta Releases, then Release candidates. During this time it would be the right time to test the software before its release and report any bugs, security issues or issues with a11y, so it can be corrected until the final release.
Unfortunately, there are many users out there that just use Limesurvey but never give back. Resources are limited and testing seems to be highly unpopular with users. It is always a struggle to get enough people to test the alpha and beta releases, as well as the release candidates.
So I can understand that the focus is first focused on bugs that block usage for anyone and a11y gets on a back burner. This might be sad, but unfortunately this is the situation. If you want to improve this, ask your colleagues and users to test as much as possible before each release. Setup a test environment and let them try to break it. At the end of the day, the software is provided for free. I feel the least we can do is help the developers where we can with translations, bug testing, etc.