Regardless of whether it's designed to shorten the game, it lengthens it significantly. Monopoly only ends when enough money leaves the economy. With the free parking lottery a LOT less money leaves the economy, leading to extended play time.
> Monopoly only ends when enough money leaves the economy.
Not true. Monopoly ends when one player can take money from others faster than they can accumulate it. There can still be net money into the players, just not net money in to most of the players.