database design – why do we need different type variations to simply represent a byte byte storage chain?

I am learning globally about databases. At a MongoDB webinar, he said:

Inherited types such as char, varchar, text, clob all kinds of
the variations to represent a chain suggest a very strong coupling
at bytewise storage concerns.

Can any one help me understand why we need all these types of data to store strings in a byte-by-byte storage? Thank you