This is cultural. In Polish there's separate word for n-hundred. 200 is dwieście, 300 is trzysta, etc. So nobody thinks about number of hundreds and tousands as connected thing, we just divide the number differently because of language.
Imagine someone told you "twelve tens" for 120 :)
Anyway, "tysiąc dwieście" for 1200 is easier than "twelve hundred" or "dwanaście setek".
As a German watching some English podcasts I am now used to it, but at first I pictured the trailing zeros in my head to understand it fast enough in spoken language.
I think it's an American English dialect thing. I'm from Ireland, a dialect close to British English, and always found it odd when they say it on US TV
Depends on the language. In some, "one thousand two hundred" is about as simple as "thousand and twondred", while "twelve hundred" is "twoovertenhundred" and quite a mouthful.
I use it all the time. What's easier to say, "one thousand two hundred" or "twelve hundred"?