Compatibility with Existing Standards
Some frameworks attempt to simplify your work as a developer by providing you with tools and functionality to wrap around common tasks, such as making network requests or managing data submitted by forms. While the intentions are noble, this strategy can have unintended consequences. For instance, when learning a new framework, developers have to master all of its intricacies to be effective. Reading about yet another way to make network requests can slow developers down, as time spent reading documentation is time spent not building. It can also prevent code portability. When the code written for application A is specific to framework X, then the code will need to be modified before being reused in application B, which was built with framework Y.
SvelteKit has a solution to this, and that solution is to do nothing. Well, not nothing, but rather than providing you with wrappers and functions that will require you to look up the documentation...