<p>I’m a prof and often “I don’t have time to supervise your thesis” is what we are told to say because we’re not actually allowed to say:
-I don’t think you have what it takes to write a thesis, since you’ve never met a deadline in my class and you always ask for an extension and believe that the rules don’t apply to you.
-You don’t take criticism well (or at all) and therefore you represent the advisee from hell
-You are extremely wedded to your own opinions and are not open-minded enough to do good research.
-Your politics offend me
and so forth.</p>
<p>You need to at least consider (along with your son) the possibility that “I don’t have time” is actually code for something else. Has your son struggled to meet deadlines? Does he frequently ask for special treatment or refuse to take criticism? Is he a strong writer and researcher? Is he teachable?</p>
<p>At this point, I’d recommend that your son go to a professor and very bluntly ask this question: I notice that many professors have stated that they don’t have time to mentor me. Could you perhaps provide me with some more feedback – is there something in particular that makes me seem like writing a thesis would be problematic for me?
Then you can work with a professor to map out a strategy to adjust any perceived deficiencies and perhaps convince him or her that the thesis should be an option.</p>