The "like an adult" is what has and will continue to hold back linux on the desktop. Always gatekeeping less technical users instead of acknowledging adoption and ease of use are critical.
A lot of those scripts are wrappers around package managers. Creating them is extra work for distributors, but they still do it because package-manager installs are not truly one-liners and offer far less control over the installation experience.
Users need to figure out which of the 10+ package managers they should be using, then run several commands. If something fails, the error messages are often cryptic and not easily configurable by the distributor.
And that’s before getting into the many rough edges of package managers. Most of them flat-out refuse to handle configuration and leave that part to the end user. Now you also need to document how to edit YAML and restart a systemd service. With an install script this is also solved.
For power users, this always looks trivial. In practice it raises the barrier to entry and can meaningfully affect adoption if your product is often used by less technical people.