I think they wanted to give you a different type of machine gun. Maybe they thought since every other type of gun in the game had more than one kind except the TMP they should give you another type of TMP.
Resident evil 4 only had a TMP as the only machine gun in the game. I thought there should of been more types of machine guns. Im not a fan of the chigaco typewriter as they made the gun too powerful and too easy to kill an enemy with. It only took like 2 bullets to kill a ganado. So really the TMP is the only machine gun in the game you can use Thtas not superpowered.
I feel that, if they had tried to make it a normal gun, its purpose would have been to be a stronger TMP with more drawbacks, but they found that the TMP is pretty much as strong as a TMP weapon should be and made is a bonus/super easy mode weapon instead with exxagerated stats. If the TMP does 18 damage every second, the CT would probably have been somewhere around 18 or all the way up to 25 or something. It just makes the game too easy. And what's cool is that since people don't think they have anything to compare the TMP to, they think it sucks, but they are wrong.
"Maybe I'm not yelling loud enough... On earth, everybody is always looking for a giant squid! On my planet - " - Zoidberg