Exactly. It's one of the cruxes of the typical employment structure. Almost every person who advances by being excellent in their field of expertise (sales, engineering, marketing, accounting, operations, etc.) is expected to be a competent and effective manager as well. Management skills are not generally taught much, if at all, and often leads to poor performance as a whole. Not everyone who excels should be a manager, as they often operate on different frequencies so-to-speak.
Well, to be honest, I'm not sure that whether one has a BA in Engineering has much to do with it. Hell, even elementary education (not a dig at that) will show enough aptitude to be able to run a company. Running a company when small isn't much of a game in mental gymnastics once you understand how a basic set of financial statements work. The problem starts when an engineer (or any profession) is really good at being an engineer, but suffers from not constantly evaluating the bottom-line for a project or proposal. Engineers often love to get enveloped in their work, and may not always be able to separate their enjoyment of a project with the profit/payback aspects.
More than 50% of business start-ups fail in the first 3-5 years, and those include businesses started by intelligent engineers. Developing a sustainable business strategy, creating a niche product, sourcing customers, understanding cash flow/tax effects, etc. all play a role in whether a business succeeds, not to mention external factors. In theory, tons of people with advanced technical degrees should be adept at running their own businesses, but history shows that in practice, it doesn't always translate so easily.