Portal series writer Eric Wolpaw approached Valve Studios with a request to begin work on the third installment of the franchise. The developer justified his impulse by the fact that time is running out, studio employees are aging, and therefore you can no longer waste precious time.
Recall that the first part of Portal was released in 2007, and the sequel appeared in 2011. More than a decade has passed since then, and now the era of re-releases and resurrections of franchises that were previously considered complete has come. By the way, Valve recently refreshed the legendary series by releasing a small project Aperture Desk Job, demonstrating the capabilities of the new Steam Deck portable console.
Although, of course, Portal fans are waiting for more serious development.