Because there are several types of Arabic handwriting in its calligraphy form. This specific one is called "althuluth". Very famous and beautiful form of it.
That's an old writing called "Koofi". The name comes from " Koofah" a city in the Iraqi province "Najaf" where a lot of this art originated from. This is a very old form of it (precisely, during and before the times of the start of Islam in the year 600 AC).
I'm actually an Arabic calligraphist myself. Been doing it since I was about 7 years old. I'm now 43 and I still practice. It's become like an addiction to me. I even had a shop at some point of my life where I made shops signs and other things like those announcements they made when someone passes away (sorry don't know what they're called in English). I even made some decent money, too. I still have my read pieces and inks now here in the US.
That's amazing and you sound like you've had a cool life. I really respect your craft and the art you've made. Also I think the word you're looking for is obituary.
Thank you so much. I can't say that my life was cool per se, as I lived it as a shephard/farmer. It was extremely rough. You could say it is cool when you look back it at now, but not then. We didn't have power back then, so my only entertainment was my craft and reading books. I'd go for hours, after a full day of work in the farm and taking care of our cattle(sheep mostly), writing and practicing or reading. I can't even count the number of books I have read (all non-fiction, BTW). Also, thank you for the word "obituary". I've learned a new word today and I always appreciate that :)