Why does the Metroidvania genre refer to Symphony of the night, rather than Simon's quest? [closed]

Solution 1:

Because Symphony of the Night is considered by many to be the definitive Castlevania experience and an exemplary game of the Metroidvania genre.

While some of the elements that are considered to be part of the genre were introduced to Castlevania by Simon's Quest, Symphony of the Night drew inspiration from Simon's Quest and expanded and improved on these elements. Symphony of the Night offers a more complex and intertwined map to explore, a greater diversity of abilities and weapons, and delivers an experience much closer to how we view games of the genre today than Simon's Quest.

SotN also had a much better critical reception than Simon's Quest, and is remembered much better. In addition to redefining what to expect from a Castlevania game, it was also considered to be one of the best games of the era, receiving universal praise and placing on several "best games" lists.

In a nutshell, while you could point to the earliest work possible that shares traits of a genre, it is often more useful to start with the best known or most obvious examples to define it. While the first examples of art were cave drawings, if you wanted to explain how we currently think about visual art it is probably more helpful to use renaissance or more modern paintings.