That is because Linux Mint uses Ubuntu Repositories as it is based on Ubuntu, as well as any other Ubuntu based distribution, for me, nothing special but good to have. The difference with them are the community and the DE.
Kevinsotovalle ¿Why should I stay with Solus OS and not change to another?
I think that's a personal opinion, the best I can say is to try it for a week or a month and then you can make an educated decision, nothing is perfect. My experience is very good, simple to update by the software center (gui) or by terminal, with the option to use Budgie, Gnome, Plasma or MATE and they are very stable, I use Budgie and It runs as good as my pc can, no mayor breakages in more than three years of use in my machine. Did I mention Solus install process is fast and boot fast?
Kevinsotovalle ¿What are the advantages and differences of this distribution?
Advantages?
I should mention the curated repo, it's not big compared to Debian, Arch, Fedora or other "mother" distros but it have everything a normal user, developer o "gamer" would need.
At the same time, Solus support Flatpak and Snaps, if isn't in the solus repo I'm pretty sure it is in flathub or snaps.
Kevinsotovalle ¿What are the advantages and differences of this distribution?
Direfences?
The first thing you'll notice, it's no based on Debian, Ubuntu, Fedora, or any other distro, Solus is independent and don't rely on other distribution or company.
Updates are every weekend Friday night depending on your time zone, and as they say, "Install today, updates for ever". Solus is a curated rolling release, kind of what fedora does, every Friday are updates, if there are new kernel release on Sunday, the next Friday will probably be on repos, the same for every other package.
Packages are maintained by the core team (Solus developers) and the community, mostly volunteers on their free time.
You can download solus here: https://getsol.us/download/
Learn more about to who is solus targeted for: https://getsol.us/solus/about/
Solus history (update post): https://getsol.us/blog/
A help center https://getsol.us/help-center/home/
And if you consider to get involved: https://getsol.us/articles/contributing/getting-involved/en/
I'm a very long time Solus user, since the first release.
That's all from me.