Too often that isn't possible. There is a lot of domain knowledge in making a widget there is a lot of domain knowledge in doing a job. when e complex job needs a complex widget often there isn't enough overlap to be experts in both.
sure 'everyone' drives so you can be a domain expert in cars. However not everyone can be an astronaught - rockets are complex enough to need more people than astronaughts and so most people designing spaceships will never have the opportunity to use one.
I am not asking anybody to be an expert in both (although I am sure such people exist, however rare); I am saying people should ideally have some skill in both. Also, people can collaborate, and learn new skills.
If you're bottle-necked by waiting for the users of your product to give a feedback, you clearly need to spend more time learning how to be a user yourself. Or hire people with some domain skill who can also code.
sure 'everyone' drives so you can be a domain expert in cars. However not everyone can be an astronaught - rockets are complex enough to need more people than astronaughts and so most people designing spaceships will never have the opportunity to use one.