It’s just a way to make bash installers more secure.
bash installers from the developers, and vendored/pinned dependencies in general will never be secure for the reasons I mentioned above. Developers are bad at security. Developers should not be installing software on people's machines.
There are clear alternatives to using developer install scripts to install software though: package managers
Developers incorrectly believe that they need to vendor dependencies or control the way software is installed, which package managers of distros do not offer them. So they don't mention the way that their software (deno, rust) is packaged in nixpkgs, and instead mention the install script. Actually Deno mentions nixpkgs, and Rust mentions apt on their less immediately visible docs, but the first recommendation is to use the install script.
The core problem mentioned here is one of packager control vs developer control. With an install script that downloads a binary (usually vendored) the developer has control over things like: the version of the software, how it is installed, and what libraries it uses. They like this for a variety of reasons, but it often comes to the detriment of user security for the reasons I have mentioned above. Please, please read the blog post about static linking or look into my cargo audit. Developers are not security experts and should not be allowed to install software, even though they want to and continue to do this.
One the other hand, with package maintainers, they value the security of users more than things like getting a new version out. With package maintainers however, they take control over how packages are installed, often using older versions to dodge new security vulnerabilities, at the cost of keeping the same set of non-security related bugs, and sometimes the developers whine about this, like when the Bottles devs tried to get unofficial versions of bottles taken down. Bottles even intentionally broke non-flatpak builds.
But I don't care about developer control. I don't care about the newest version. I don't care about the latest features. I don't care about the non-security bugs not getting ironed out until the next stable release. Developers care about these things.
But I care only about the security of the users. And that means stable release. That means package managers. That means developers not installing software.