Here is another example of vendor abandoning patching. From time to time businesses around the world would have to make those decisions based on simple economy, however I think it would have been honest from their perspective is to open source their code, so that community could fix it. Unfortunately that's not the case for any of the vendors, luckily people have choices there is OpenWRT which is an open source ecosystem for routers, and that model is supported.
https://www.howtogeek.com/d-link-dir-856-router-exposed-to-hackers/