Why not store types in global d.ts file?

In lesson 16 of the final section in part 2, we refactor to move types/interfaces into an entities folder. Back at the beginning of part 1 I put my types in @types/index.d.ts and set my tsconfig.json file to include these.

"include": ["src", "src/@types/**/*"],

I moved FetchResponse to the api-client because it makes sense that it is part of the api service. If we created separate services for genres, platforms, and games I could see moving those types there.

But my question is, is there a good reason not to just put them in a global .d.ts file like I have done? What is the downside (if any) of having these types available to the entire project in this way?

Thanks for any input