I partially disagree.
Boeing has a system that should alert the pilots if the engine cowls are not properly latched. It is not clear at this time, and we may never learn, if this warning system failed or was ignored.
There is no system on a Boeing 737 with CFM 56 engines that alerts the pilots if the engine cowls are not properly latched. The cowlings that departed the aircraft are called the Fan cowls. The cowls latch to each other along the bottom edge.