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This is really owed to the display technology. With prices of memory for a bit plain frame buffer in the astronomic regions, early computer displays were x/y displays, often just plotting single dots. So any visuals were generated on-the-fly. (Text was generally put out on another media, namely paper.) While Computer Space had a raster display, it generated its graphics also on-the-fly by means of circuitry. In both cases, displaying text was complicated and added another layer of complexity (and was also more time critical).

I think a good text game is actually incredibly complex compared to the simplest types of graphical games.

Yes, in the early 1980s text adventures by Infocom were high-end computing compared to every other type of game.

These adventure games were developed on a Unix minicomputer and executed in a custom VM that could fit both the engine and game onto 48-64k RAM available on the microcomputers that customers had.

Graphical games don't require that the author can spell.

I'm guessing you meant "were" not "where".