Actually, I believe that used ebooks can sell for almost the same price as "new" ones. Unlike with physical books, there is literally no difference in reading experience between an ebook that has been sold a hundred times and an ebook that's new.
However, as someone who reads books and who would appreciate a right for resale for ebooks, I don't appreciate it for being able to make money from reselling it. I am more interested about the effects: that I have actual ownership over the ebook. That the place which sold me the ebook going bankrupt doesn't disrupt my abilities to read it. That I can lend it to a friend. etc.
Now, if you allowed resale, ebooks would have close to "new" resale values, and more importantly, resale values of ebooks which have been sold three or four times would stay the same. This would create the problem that people could buy an used ebook, read it, and then resell it afterwards for the same price, basically reading the ebook for free. Now libraries are doing something similar with physical books, but they are inconvenient to use. You need to get to the library, stand in queue, handle the books, think about bringing them back in time, etc. But ebooks don't have such limitations and you could build a super convenient solution around ebook lending. While it's great that people read books, it's sadly not really good for publishers or authors. I kinda understand them that they want to close this loophole. Still, you could allow for resale in some different fashion. E.g. a resale tax of 10% of the value or something. In my opinion that would be the optimum, and a solution that's fair to everyone.