no idea,,, i think its pretty great. Just bad luck on which reviewer you got perhaps?
its a good work,but sometimes they reject strangely!
Font choices are all over the place, use 1-2 similar fonts, perhaps one with nice variations for some contrast.
Color/style looks pretty dated, and there are already plenty of lower third templates that look like this (probably the main reason it was rejected)
From the preview it looks like it was pre-rendered lower thirds vs an editable AE project, I think that is another reason it was rejected, most folks want to buy something that’s editable rather than something that’s not.
Lastly, the overall design of the lower third elements isn’t that bad but I would have animated the individual components rather than just slide them all in, have that 3D looking red bit actually animate and wrap around, that would have added some detail that would look nice.
Keep at it, all we can do is get better!