Video games aren't like other forms of entertainment. Paul McCartney's old albums are regularly updated for new mediums (tapes, CDs, etc.) and are fundamentally comparable to new albums made today minus some audible differences in production.
A video game made in 1988 may still be great, but there are much higher barriers to it finding a modern audience:
1. It may be difficult to run on modern systems (or at least require a level of knowledge -- e.g. what is ScummVM -- that makes it harder to access than a modern game for the uninitiated).
2. It may be so dated from a graphics, interface, or gameplay mechanics perspective that someone coming to it fresh will not enjoy it.
3. It may not even be possible to legally acquire; unlike movies and music, where old releases are often available alongside new releases, old games disappear from shelves.
Sure, there are exceptions. GOG.com, ScummVM, buying something on Ebay. But you have to already have an interest in exploring or revisiting older games.
Game designers are celebrities within their field, not within society. Paul McCartney is a celebrity because of his musical contributions, but he also is immediately recognizable to millions of people who may have never heard his music. Richard Garriott is a celebrity only to people who know his work -- which, as mentioned, has not continued to be relevant in recent gaming history.
And that in a nutshell is why someone as important to early gaming history as Richard Garriott was may not roll off the tip of someone's tongue today.