If this has been posted, apologies, I looked and didn't find it. I just thought this was very interesting.
I've seen this discussed several times and it usually comes with lots of highly scientific and technical answers, but check this out. I took the lens hood from my 70-200 and put it in front of my 24-105 (no, it won't fit on it) and took a picture.
Quantum Physics & Light theory aside, the reason is obvious:

