Completion Time Estimates

I currently have seven designers working on eight different projects.

Of these one is not due yet
One was completed today only a week behind schedule
One did not set a time frame deliberately (and that is OK in this case)
One did not set a time frame but carefully stays in touch and updates

The other four are all late...

This of course throws off *my schedule*...especially when I am doingthe work for someone other than myself.

I have at times waited as much as a year from the expected delivery date.

My sense is that this happens for three reasons:

1. Some designers take on too many projects at once in hopes of making more money

2. Sometimes things come up that requires more time than anticipated by the designer (and they tend to put it off and do the ones they can complete mpre easily)

3. Life happens

What I find most frustrating is the tendency of so many to simply disappear when they are pressed and behind schedule

What are your thoughts on why this happens so often?
What can designers do to improve this situation?