Transportation engineers abound at the Department of Transportation, which has always been led by politician/managers like Elizabeth Dole. The same applies to almost all cabinet-level departments. They're managed (on purpose) by politicians the president appoints, not by technical experts.

Setting priorities, goals, etc, in cabinet departments is an inherently political function. Cabinet secretaries serve at the pleasure of the president in order to ensure the president's political goals stay in focus in the department. That's basic "separation of powers" that's built into the system via the constitution.

Now, if Buttigieg were firing all the transportation engineers in the department or not heeding their advice, you could legitimately claim a problem and ask the president to replace him. But nobody is claiming that. They're simply saying Buttigieg is unqualified for not being a technical expert -- when he was never supposed to be.