In an old comment that I can't find, dang explained that the problem of enabling the comment section in the job posts is repetition. Jobs post of each company are very similar, and they may even be equal if theay are hiring a second person or the first try didn't get any candidate. So everyone that likes the company will repost the same comment, and everyine that dislije the compay will repost the same comnent, and the result will be the same discussion again and again each time.

If you are interested in what they are doing, I sugest to look at their blog and pick the most interesting article (in your opinion), and post it to create a new discussion. (You can even post the first commemt to sugest the topic you want to discuss.)