Take a look from this perspective: with distro packages, a separate person (the package maintainer) has to build a piece of software against the versions of dependencies the distro offers, which are not the ones the developer of the software uses and tests against. Then you have users that encounter bugs with this build of the software, and the developer of the software receiving bug reports against all kinds of dependency matrices, whose combinatorial complexity is overwhelming. With the different paces of distros in terms of package versions this is inevitable. On top you have overworked package maintainers which leads to sparingly updated distro packages or even orphaned ones.

For no party in the linux ecosystem this is a great experience.

Either it is this, or giving packages the opportunity to not share dependency versions, which can cost a bit of disk space. With the low price of storage, I think it becomes quite clear why flatpaks are so popular. Also in the end, users do not shape the linux landscape like they would with commercial products, as distros do not rely on sales to users. Developers and maintainers shape the landscape, and so what floats their boat is largely what happens.

For linux as a whole, flatpak is one of the greatest things that ever happened. For the first time, one can treat it as an actual platform, and that makes it a strong ecosystem.