Ignoring bugs, the main problem with this game concept is something called "kiting." Kiting is a movement style which can be used in many games to group enemies together by circling the group. Because paths of pursuit tend to naturally converge on the object of the pursuit, zombies that always move in the direction of the player will ultimately end up grouped together, rope or no rope. If you want players to have to use the farmer's key ability, you have to remove the ability to kite.
This can be accomplished by giving each zombie a slightly different movement pattern (i.e having one zombie always try to move towards where the player will be, while a dumber zombies moves towards where he's been), making their movement more erratic and staggery, and making some zombies faster than others.
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Agreed. Thank you for the helpful comment!
I had debated spending more time on the zombie movement but given it's a jam game it felt nice to allow the players to use their kiting tactics if they preferred instead of forcing a certain playstyle - it's certainly requires a bit more patience! Given more time however we absolutely would have added more to their movement (and have different types of zombies for more variation again) to absolve that issue and encourage use of the main rope fun