Plenty of software companies provide their own Apt repositories. Adding a repository is usually as simple as copying a single file to /etc/apt/sources.list.d/. Sometimes you may also need to add a GPG key, which can also be as simple as copying a file to /etc/apt/trusted.gpg.d/ (though most instructions seem to favor a manual one-liner that imports the key to the global database[1]). Technically you could automate both with a one-time deb install, though I'm not aware of anybody that actually does this. In any event, after that `apt-get upgrade` will upgrade third-party packages just as well as Debian or Ubuntu packages.
I much prefer Debian packages over RPM, and Apt over Yum/DNF, but unfortunately setting up a Debian package repository is more difficult than for RPM. The tools exist, and are more sophisticated and capable--for example, Aptly--but there's a higher learning curve. Also, good luck using them outside Linux. Years ago I published Debian package repositories from OpenBSD, but I had to manually hack the relevant tools to build and work on OpenBSD. For RPM/Yum I could have more easily written (and at a different job later did) an indexing tool from scratch.
The problem with Debian packages and Apt repositories isn't that they're not capable, it's that they have high learning curves due to the slow accretion of features that obscure their potential. A better tooling story would help, particularly for repositories. Better tools for initializing Debian package builds exist; the problem is more a surfeit of choices.
[1] It's more complicated and creates unnecessary headaches than dropping a file into trusted.gpgp.d, but the practice seems to reflect the opacity of the Debian packaging ecosystem. There's a better, simpler way to do it, but everybody cargo cults the same old solutions and then complains that it's too complex or inelegant.