From installing a library, to browsing logs. From reading documentation to deploying code. Everything in the developer experience is mined with obscure processes and seemingly impossible to achieve tasks. Every developer eventually figures out a mental framework to work around this experience and consider this a skill that it's part of what makes them good at their job.
Of course developers are very smart, so why they "suck at ux"? The problem is that when your tools and processes are full of bad UX patterns you never get an opportunity to really learn and analyze how well-designed professional and productivity software works. I can't tell you that 60%-70% of the things I know come from using software (many times using it for the sake of learning its UX, not because I'm an actual user). Basically, exposure is key and this is why there are UX designers that also suck at their jobs.
Developers are trapped in this loop. Homegrown tools rarely include input from designers. Startups in the developer space rarely prioritize design hires. They can only build and try to improve what they already know, so the progress in developer experience is very slow. Any progress depends on companies like Microsoft investing in design. For example Visual Studio Code is a wonderful developer experience in my humble opinion. But it takes more than a good IDE or text editor to create that instinct to identify what's good or bad UX.
I wouldn't say that developers suck at UX. They are just not very good at articulating their UX ideas, but some of the best things that I have designed even outside of the developer tools space, came from a developer idea.