This is even worse with managers. Managers have whole lot of other problems to deal with and what they frequently fail to recognize is the need to separate areas where it is up to manager do act on their "instincts" (which I call experience) and where it is up to engineer to do their job.
Unfortunately, the power assymetry between managers and engineers frequently manifests itself as you have described:
-- managers trying to understand everything through the lens of their past experience,
-- engineers trying to conform to managers (ie. using manager's language to formulate problems and solutions)
-- managers dismissing/prioritizing down areas, ideas, problems that they are not familiar, promoting/prioritizing up where they feel they have good understanding,
-- engineers responding by doing the same (ie. focusing on where they feel they will be rewarded by manager).
-- managers hiring/promoting based on their assessment of the candidates/employee competency in the area of expertise of the manager, because it is easier to rate candidate/employee competency if it is in your area.
-- managers failing to improve in areas where they are completely new. Maybe because people in general tend to want to improve in areas they already know. Maybe because they don't want to be seen as noobs making silly mistakes with experts around, and so trying shun entire area as less important so that the discussion can focus on where they are comfortable talking to experts.
-- so on...
So where a team works on a product that requires software/electronics/mechanics, the team, regardless of its initial composition, will over time get skewed in the area of expertise of its top manager.
Same goes for startup -- duo of guys who know software and electronics will inevitably look for products in the areas they know best. Not being able to quickly rate how difficult something is, mechanically, is definitely scaring a lot of people away.
I also noticed people dealing with software and electronics rarely mingle with mechanics/material experts which I think might also explain a little bit why there aren't too many enterprises that join those areas well.