Look at installing Gentoo, or Arch, or Alpine vs Ubuntu. There’s no technical reason we can’t make Gentoo installation GUI. It’s just going to be very very tedious. Orders of magnitude more tedious.
At the same time Gentoo allows you to customize WAAAAY more things during its install than Ubuntu.
So specifically for lemmy - yeah we can probably make some sort of default AWS image where you just select it when spinning up new VM and you’re up and running. But what if you want something slightly different? Maybe you prefer MySQL instead of Postgres. Or Apache instead of nginx, or maybe you want images hosted on a different machine. Suddenly it’s the install GUI author’s responsibility to support install of 10 different databases, or load-balancers, or something else, and each one has their own GUI options. Then someone else wants 11th database added and it has 10 more custom options…. Oh and now someone else is asking for a DigitalOcean image instead… or and now someone’s asking for Docker image… You see where this is going.