Because you think 3 is a fun season.
Because you think 3 is a successful season.
Because 3 doesn't hamper you on your 1600 acres.
Because only a few hunters were killing more than 3 anyway.
Because it works for you...you think everyone should abide by it? What's wrong with chosing 4 then? Some people would meet all thase criteria by killing 4 bucks some years.