Other MP3 players existed, but flash media was too small. Other hard drive players existed, they were too big. And both had bad interfaces (by Apple standards).
Apple didn’t show up until they could meet all their goals.
They could have made a phone sooner, it wouldn’t have been the iPhone. They could have made a headset sooner, it wouldn’t be the Vision Pro.
They set their standards for what’s necessary and wait to be able to deliver that.
The first mover rarely wins in the long run.