The MIDP high-level UI API was designed for applications portability, employing a high level of abstraction, however it provides very little control over look and feel, and sometimes, this is very important.
In the other hand, the low-level UI API provides a good control over graphics and input events, but the API lacks of UI components.
The Java UI's (AWT) would be a solution, but it was not included because it was designed and optimized for desktop computers.
MWT comes into the scene providing an UI framework designed and optimized for small devices.