Jacob Girdler joined Roblox on a whim more than a decade ago when he was 9 years old. The entrepreneurial teen, who largely works alone, has now designed over 300 games for the platform.

In fact, in 2023, five old games—Fortnite, Roblox, League of Legends, Minecraft, and GTA V—accounted for 27% of all playtime in the year. It gets worse. Of the 23 percent of playtime spent in ...