Why are upgradable packages not upgraded?

Executing sudo apt update ended with

Reading package lists... Done
Building dependency tree       
Reading state information... Done
2 packages can be upgraded. Run 'apt list --upgradable' to see them.

Executing apt list --upgradable gave me

Listing... Done
onionshare/bionic,bionic 2.2.ppa1-1 all [upgradable from: 2.1-1]
ring-all/unknown 20190927.2.c2af011~dfsg1-1 amd64 [upgradable from: 20190629.2.c07ef23~dfsg1-1]

But executing sudo apt upgrade does not upgrade the upgradable packages:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

1. Why is that? Unmet dependencies possibly?
2. Can I (manually) upgrade the listed packages, and if so: how?

Update: See this pastebin for a full transcript.

In this case “upgradable packages” are actually not upgradable because they have unmet dependencies.

To reproduce: try to update the specific packages in question (see How To Update A Specific Package In Ubuntu) by executing sudo apt-get install --only-upgrade <packagename>. If any package has unmet dependencies, the upgrade will fail due to

E: Unable to correct problems, you have held broken packages.

Upgrading these packages would require to resolve the unmet dependencies. Information on that can be found in the answer to “How do I resolve unmet dependencies after adding a PPA?” and “Fixing Unable to correct problems, you have held broken packages”.