With these kinds of questions, a great place to start is to look at the Debian Package Tracker. You will often find a lot of clues for what the blockers might be.
Here’s an example for MariaDB 10.4.
The takeaway here is 3 errors, 363 warnings, and the package never migrated from Experimental into Testing or Unstable. So it didn’t get picked up by Ubuntu (that’s good, it’s a bit of a mess!) Fundamentally, this kind of multiple-error in a package means that the volunteer Debian Maintainer needs more volunteer help. Volunteers like you.
Now let’s look at MariaDB 10.5:
Here you can see lots and lots of problems: Build failure, regressions, policy violations; plenty of work for volunteer help! Nevertheless, the package made it into Debian Unstable…too late for Ubuntu 20.10. Look for it in Ubuntu 21.04
Imagemagick is a little different.
The tracker page shows loads of problems that need to be fixed; definitely a volunteer-help-wanted situation.
But among those warnings is…
… and we know that’s stale because the download site for imagemagick has…
But it’s only 12 days stale. Debian doesn’t check daily. If it goes over a month stale, then feel free to do a bit of digging and then contact the Maintainer with your results. Sometimes upstreams change their site layout or made some other change that fools the Debian update script.