Its because tk does not have a central event loop built in. You can't use modern programming techniques without building up a significant scaffolding to get multiple UI elements updated based on an events generated in various places. It requires an observer pattern + a self defined callback event generation scheme to collect events (singleton pattern).

Sure you can make this module and there are probably things out there, but you need to wire it up yourself before you even get to the application logic.

This makes no sense to me. Tcl does have a central event loop. I'm not sure what you mean by "building up a significant scaffolding" - the event system is powerful enough and flexible enough to support all kinds of uses. :-/