Sierra and Lucasarts both turned to the same strategy of writing a VM for graphical games(AGI, SCI, SCUMM) and those engines basically remained viable for as lo

Sierra and Lucasarts both turned to the same strategy of writing a VM for graphical games(AGI, SCI, SCUMM) and those engines basically remained viable for as long as those companies made adventure games - when they exited it was because of the business changing, not the technology. With Infocom, I think the issue really was mostly with business fundamentals. The investment in Cornerstone turned out to be a product that didn't work well enough, and wasn't really within their existing business - and subsequently they couldn't keep up as the average cost of games started inflating to incorporate more audiovisual content. But Z-Machine probably could have stuck around and adapted if Infocom had survived that period and restructured around the trends to make their games more elaborate and movie-like.