For the most part the distros are all the same, they just configure things differently from the start or come with different packages installed. Think of it like doughnut shops, you can go to two doughnut shops and they might look a little different, be laid out a little different, ring you up a tiny bit different, but under the hood it's still a doughnut shop, a place selling fried dough rings.

The fried dough rings are the Linux kennel, the core of every distro, the color of the glaze is the distro, the "fluff" on top. You can scrape the glaze off the doughnut at one shop and put new glaze on at the other so it's a bit different, but still a doughnut.

I feel like that analogy got away from me.

So yeah, you're not really missing anything. Some people like Arch because it comes with way less preconfigured/installed so it's easier to make it exactly what you want. Newbies (I use this lovingly here) don't really care if they're using X11 or Wayland (the libraries that power how the desktop actually displays programs, sort of, massively simplifying), so they don't need Arch, they can just install a "newbie" distro and be happy. You could strip your Linux mint down to the bare bones and basically make it Arch by using a different package manager and stuff.