Why do some managers suppress new and creative ideas coming from their staff?

managers suppress creative ideas for the following reasons

1.  Superiority complex

2. perceived threat of the employees advancement higher than the manager's

3. risk aversion because: if the creative idea does not work then responsibility lies with the manager to avoid such risk

4. unorthodox nature: managers higher in age tend to shoot down creative ideas due to their unorthodox nature which the manager himself is accustomed to

I agree with Syed, it is mainly protecting their own interests. However I think they are just as likely to have an "Inferiority complex" as a "superiorty complex". Anyone confident in their own abilities wouldn't have to resort to "supressing" their subordinates.