Frame 1-4 are all the same so it changes to 1 frame but with 40 milliseconds instead of 10 milliseconds per each frame.
frame 5 then become frame 2 (10 milliseconds)
frame 6 and 7 get merged as they are the same and changed to 20 milliseconds and to frame 3
frame 8 then becomes frame 4 (10 milliseconds)
and 9 and 10 become merged as they are identical (20 milliseconds frame 5)
Unless you make a change on every frame it will make it less frames.
If the change per frame is very little it can also get merged with optimization settings.
To do this manually rather than having every frame at 10 milliseconds , you can right click the frame and go to frame properties and change the given time that frame should show.
Newer animation programs don't merge duplicate frames together as internet connections are much faster and cope with large downloads.
Hope this helps
