I'm wondering it too. probably they get rid of them and replace that section with Edge (chromium based) extensions. Edge classic will be only available inside Windows 10 OS for compatibility purposes so I don't think the extensions will be necessary.
Hi again, Microsoft posted an official answer to your question:
As we move towards the general availability of the new Microsoft Edge on January 15th, 2020, we will no longer accept new submissions for Microsoft Edge Legacy (EdgeHTML-based) extensions after December 17th, 2019. We will continue to accept updates for your existing extensions.