But what is a trusted provider? How can you trust it? How sure are you that you're not being MitM? Have you fully manually verified that there's no funky flags in curl like -k, that the url is using SSL, that it's a correct url and not pointing at something malicious, etc, etc, etc. There are a lot of manual steps you must verify using this approach, whereas using a package manager all of them get checked automatically, plus some extra checks like hundreds of people validating the content is secure.

To do apt get from an unknown repo, you first need to convince the person to execute root commands they don't understand on their machine to add that unknown repo, if you can convice someone to run an unsafe command with root credentials then the machine is already compromised.

I get your point, random internet scripts are dangerous but random internet packages can also dangerous. But that's a false equivalence because there are lots of safeguards to the packages in the usual way people install them, but less than 0 safeguards to the curl|bash. In a similar manner, if this was a post talking about the dangers of fireworks and how you can blow yourself up using them your answer is "but someone can plant a bomb in the mall I go to, or steal the codes for a nuclear missile and blow me up anyways".