The roof isn't removable... when I think of Targa I imagine the image below. Fully removable roof panel and the vehicle will have a semi convertible side profile.

Someone please explain to me the logic of why it was introduced?

 

Porsche 911 Targa-looking is what it's supposed to be.

 

i'lol'd when the example car isn't a Porsche. in short Porsche sort of made it up, the 911 had the band because it was thought with safety standards inbound that the convertibles days were numbered.
" Porsche got the name "Targa" from the Targa Florio, the road race in Sicily where Porsche was very successful. Targa means "plate" (or placard) in Italian."

https://en.wikipedia.org/wiki/Targa_top

if you wanted to go a step further, the Rx7 had the "targa band" which made it look like the 911 Targa. which was cool in the 80's

 

That is a "Targa Band". Actual RX-7 targa tops are removable (not factory obviously).