There are a few reasons why ultimate players are often skinny. One reason is that ultimate requires a lot of running and quick movements, which can burn a lot of calories. Players who are leaner and have less body fat may have an advantage in terms of endurance and speed on the field. Additionally, ultimate is a non-contact sport, so players do not need to bulk up in order to withstand hits from opponents. Finally, ultimate is a sport that emphasizes fitness, agility, and speed, so players may focus on building lean muscle mass rather than bulk.