That is a very biased claim. It's like saying that the PS5 is the most successful gaming platform because God Of War: Ragnarök and Ghost Of Tsushima players prefer it over Xbox and PC.
Did they say it's the most successful project? Because Sony saying that the PS5 is a successful platform because players prefer it over other options doesn't seem biased at all. It's just an objective statement of fact
If you go to snapcraft.io, you can see snap being installed on many other distributions other than Ubuntu. It will not show you the exact numbers, but people willingly install it on their machines. I think that's successful.
I don't think "there exists an unknown number of non-Ubuntu machines with snap installed" is a valid metric when the general sentiment seems to be apathy. It's popular for the same reason Internet Explorer was popular -- it's forcibly installed with the default OS.
If the numbers were favorable, Canonical would release them.
What is the "general sentiment" tho? Sure, on Lemmy and Reddit communities I usually see people hate Snaps, but that's just a few thousands of people. Another metric of success could be developers maintaining their software as snaps. You will find that quite a lot of them do so.
I said "apathy", not "negative". The people who dislike snap have likely moved to other distributions, and I don't see any widespread praise considering Ubuntu's market share within the Linux ecosystem, so the most likely answer is that people either don't know or don't care about snap.
Whether or not an application is packaged as a snap is also a poor indication. Most of the software used in Ubuntu still comes from an APT repo, mostly official or sometimes a PPA. Many developers distribute their software exclusively as flatpaks, appimages, or binaries. Shit, Valve even recommends against using the snap version of Steam. By using your standard, snap would be considered an abject failure.
Snap doesn't really even have as many applications packaged as people think.
Snap's package count is often touted as being much higher than Flatpak's. However, this is misleading, as Snap allows the inclusion of many command-line interface (CLI) only packages that aren't well-suited for containerization.
The inclusion of these CLI-only packages drastically inflates Snap's overall package count, while Flatpak does not include as many standalone CLI tools.
Furthermore, packaging CLI tools as Snap or Flatpak packages doesn't really make much sense. A huge amount of CLI tools were never intended to be used inside a containerized environment like Snap. As a result, there will likely be compatibility issues and unsupported edge cases.
Additionally, there are already established universal packaging standards for CLI tools, such as Nix and Homebrew.
These packaging systems are better suited for distributing standalone CLI applications compared to containerized formats like Snap and Flatpak.