It's because ES just gives a broad concept of most things. Engineering at uni will focus a lot more on specific understanding within the courses that you do. Examples of subjects that will be offered as part of an engineering degree at most universities:
• Materials
• Physics
• Chemistry
• Maths - calculus, linear algebra, multivariate calculus, statistics and data
• Electronics/Electrical
• Software and computer systems
• Applied mechanics
• Thermodynamics
• Design projects specific to your discipline
Engineering studies is child's play compared to university, but it was only aimed to introduce you to the broader aspects of engineering.
Why not go to a few uni websites and look at the first year course lists for the types of engineering you are interested and see if the subjects interest you? You should be able to look at course profiles, assessment methods, etc