I imagine this too! So… my choices are: Postman or Burpsuite!
Postman is just so nice due to the quick and easy UI to do exploratory testing on APIs.
Most of the time I start on a project, developers are already using Postman, so it’s not only easy to use for them but easy to collab between developers & testers.
I use Burpsuite more often to easily alter/add headers, run wordlists, the intruder and test for race conditions. They also offer a lot of plugins that can be used in testing APIs, so depending on what I’m testing, my choices go between Postman or Burpsuite.