Developer cognition is the most expensive resource on any programming project. It is entirely rational to stick to tried and true ways of doing things. A developer’s mind is generally at capacity, and putting some of that capacity into learning new tricks comes at the cost of all the other things that developer can be doing.
And it’s not just a matter of time. Generally speaking, a developer can only do so much mental processing between sleep cycles.
That’s not to say it’s always bad to learn new things. In fact one has to in order to keep the system working in a changing world.
But throwing shade at developers who hesitate to learn new things is foolish. I’d recommend every developer do shamatha and vipassana meditation so that they can more accurately monitor the state of their own mental resources. Those mental resources are the most valuable and most expensive resources on the project.