The difficulty curve in Tetris has a few different possible knobs to adjust as the levels go up, generally involving how much of a delay you have on certain events. The most obvious is gravity, which is how many frames it takes to fall one space (or, to ramp that up further, how many spaces it falls per frame), but the relevant one here is lock delay. This is the amount of time between the piece landing and the player losing control over the piece. Low lock delay like you have on NES tends to make small mistakes a lot more punishing. High lock delay lets you reposition a piece shortly after it falls. Modern Tetris has a small but highly controversial change to the lock delay logic: rotating a piece resets the timer. This means you can spam the rotate button to think about where to place a piece indefinitely, a technique called infinite spin. Presumably this was done with timed and battle modes in mind, where this isn't really an advantage because it's always better to play quickly, but in endless it has no meaningful cost. So leaderboards started to get pretty grotesque, with top scoring games dragging on for dozens of hours. Something had to be done about it, and shifting focus entirely to timed and line limited modes was the choice they made for better or worse.