The crux of the problem is that all current official Debian packaging methods supported by Debian are sufficiently arcane and obtusely documented to the point that it's a high barrier to entry for people to do it right.
Personally, I've been doing RPM and Debian packaging for over a decade now, and it boggles the mind how much more complicated doing _correct_ Debian packaging is for essentially the same that happens on an RPM distribution like Fedora or openSUSE.
One of the reasons that I started using debbuild[1] for building Debian packages years ago was that I felt like I could get something that closely resembled a policy-compliant Debian package without impossible amounts of guesswork. Combined with macros adapted from Fedora and other distros[2] as an interface for Debian packaging policies, I can package things rather easily for Debian/Ubuntu using the much more straightforward guidelines from Fedora as a base.
As it turns out, it doesn't take that much effort to make packages that comply with Fedora/openSUSE Packaging Guidelines and Debian Policy with this tool, and it has drastically simplified my ability to maintain software across distributions in a way that still cleanly integrates with the distribution platform.
I wish that debbuild would be an officially supported mechanism in Debian, but it's probably unlikely without a Debian Developer advocating for it (and I suspect no one there would, as they probably like the existing system...).
[1]: https://github.com/debbuild/debbuild
[2]: https://github.com/debbuild/debbuild-macros
(Disclaimer: I am now the current developer of debbuild and debbuild-macros, though I wasn't when I first started using it)
Simply throwing a bunch of files into a package or a container is very quick.
Making an official Debian package is not supposed to be quick. DDs thoroughly review and test the software they are packaging. While packaging I often chase missing licensing information, find plenty of bugs, write systemd unit/init files and sandboxing, write manpages, functional tests, and sometimes find serious vulnerabilities.
I worked on various packaging and deploying systems, and most other distributions don't come anywhere close to this level of scrutiny.
I should also add that becoming a DD requires years of commitment and proven track record of work.
The next time someone complains that making a container is very easy in comparison they should ask themselves: how much can I trust a software source with a very low entry bar?
I dare say, if Ubuntu is any indication, Pacman packages consistently feel higher-quality than deb packages. Unlike on Ubuntu, on Arch, you can actually update your packages without breaking something...
The tradeoff you get with other distributions being quick, is less quality assurance. Also, Debian still has a policy of working on 10 architectures, and this slows things down significantly sometimes. The other distributions you mentioned don't have this constraint.