Ok. Name one?
Ropo, I would reference taste as being the main reason.
I am not looking for an argument. Realize that coffee is a very serious hobby for me, as I have what many believe to be the best home/light commercial machine (the Alex Duetto). Prior to that I had the Andreja Premium (awesome machine that I modded the heck out of, but it was not PID nor did it have a double boiler, so it was limited in that regard).
I used a naked portafilter exclusively for approximately 7 years, and it made me have a tamping technique that would work in the finest of coffee shops (if you ever want to get great beans, PM me, as I am very close friends with an individual who is revered as one of the best roasters in the world).
For whatever reason, the traditional portafilter tastes better to me. Now, there is a serious drawback to the traditional portafilter, the main one being that you have to clean the portafilter regularly, as each shot can leave residue, which also makes the basket dirty.
But to me, taste is what it is all about. You can have all of the academic techniques/analysis/etc. but for me, it all comes down to taste.