Valve didn't make those games. Ask the publisher to sell them here.

Prepare yourself to learn about another layer of licensing.

IP owner gives a publisher a limited license, publisher makes and sells game. License expires, game no longer generates enough revenue to renew license. Publisher loses rights to game, so game is no longer produced physically, game is removed from digital stores. IP owner doesn't really have much interest in aged game based on a movie or whatnot from decades ago. Game is caught in limbo.

IP Owner doesn't care about it, license is too expensive for anyone to pay for it and do anything with the game, and demand for most aged movie-tie in games is modest at best, so it's just stuck until something gives.