There's a certain accepted wisdom: homogeneity is easier for the user, because the more familiar an interface, the less mental processing
...and that lent a certain legitimacy. You looked real because you looked like everything else.
If you design for the Internet, usability is this word that you're going to encounter a bunch. And it's often treated as the go-to, toss-it-out, sole criteria for judgment on web design.
From Principles of Computer System Design: An Introduction (2009) — People are part of the system. The design should match the user's experience, expectations, and mental models.
"The principle of least astonishment (POLA) proposes that a component of a system should behave in a way that most users will expect it to behave. The behavior should not astonish or surprise the users."
The following is a formal statement of the principle: If a necessary feature has a high astonishment factor, it may be necessary to redesign the feature.