Few papers use DOIs in the reference section (example below). What are the downsides of using DOIs when listing references?
A typical example from one of the main conferences in the natural language processing field showing no DOI:
There's no downside for me, but finding them can be challenging. I just looked at several recent downloaded articles, and I don't see a DOI on the front page. So, I'd say my personal inertia keeps me from digging around on the Internet looking for a DOI to add to my BibTeX entries for each paper I want to cite. I try to add them when they're immediately presented on the papers I cite, since they do have to be found. But having to go look to find them makes them less likely for me to use. Not every paper has a DOI that is readily found. There's no step in my workflow when writing where I go through all my DOI-less citations and try to find one. Maybe that's a bad habit, but it is my habit. I suspect that's true for many authors, but I think you have a bad assumption that there's some downside to DOIs that prevents people from using them. It's not enough of a requirement yet that people do it because journals or the community demand having them on every citation so that people get over their inertia and go find them or figure out if every citation even has one.