I want to use use photoshop elements as editor in lightroom, similar to LRc, but I can only edit directly in the full photosop which I no longer use. Why can't I select PE 2027 as a default photo editor directly from Lightroom cloud?

In Lightroom, go to the File menu and click on “Edit in” (right below Edit in Photoshop).  Click on Browse in the resulting submenu and navigate to Photoshop Elements.  Once you’ve done that, you can select an image in Lightroom and open it in Photoshop Elements for editing.