Clydes, this is just guess-work, as I am no expert:

If they do have signed contracts with anyone, is this not worthy of a news release?

The usual reasons: NDA's as well as stealth mode "could" have higher importance then shareholder publicity. I think they could tell us that there are contracts under NDA with x volume and not named partners/customers. But even this could be locked under NDA. More important: It could be better that competitors or parties who could take us out for cheep (sic our SP!) are staying in the dark like us.
If such material info could kill the future of POET, it does not have to be published. No idea if, how and who can judge this...

Also, wouldn't those in the know at these companies be buying POET left, right and centre.

Possibly someone is doing exactly this, slowly, step by step without stirring up things. In addition also this coud be prohibited in NDA's.

Yes, all this is guesswork, but it makes the most sense to me. Wishful thinking?
Well, why should POET hire this bunch of experts without knowing how to finance? The only way they can now do a further PO would need them to showing contracts and a clar path with secured revenues. But exactly with this info I expect the SP to fly over the mark of 0,52 CAD  - for the warrants to be financing POET. We will see...