It's important to consider that total number of turns is only one part of the equation. You could play 2 players on the 4-player side and enter the final round when the gardener has moved 50 spaces, but the game might feel very different. Though the total number of turns per player would be the same, the ebb and flow of the central market would only correspond to the first half of a 4-player game. I suspect the interplay between these two aspects may have guided some of the decisions regarding player count differences.
I'm wondering if the 2p game feels less tense as a result.
I do suspect that Cottage Garden is a game that will never feel tense. My feeling thus far is that success is mostly down to a combination of luck mitigation and shaving grams off your plans to improve overall efficiency.