[KrishnaShripad]

Because you only want to merge two objects that have keys with string type. "object" is represented as Record<any, any>. That would mean, you can use any type as key. Here is an example:

  function merge<
    A extends object,
    B extends object
  >(a: A, b: B): A & B {
    return { ...a, ...b }
  }

  const result = merge(() => {}, () => {}) // should fail!
  const anotherResult = merge([1, 2], [3, 4]) // should fail!

Which is obviously not what you want.

This table here gives you a good overview of differences between object and Record<string, unknown>: https://www.reddit.com/r/typescript/comments/tq3m4f/the_diff...