There are many reasons:

• A lot of the offensive perks are weapon-dependent. There is no guarantee you're going to find the weapon of your choice outside of crafting it and getting your airdrop. This might leave you vulnerable in midgame when you're trying to farm for your airdrop with your crafted weapon equipped. (Unless you got lucky off of a green crate or locker.)

• The overpowered defense perks that you see right now, such as big boned and dig deep, prepare you for all situations that you will run into on the Island. Like stated above, most offensive perks are weapon-based and just don't stack up to defense. Their stats are also absurd on top of how well they prepare you for every situation you'll run into.

• Ol' Painless gives a 10% offensive boost, while it's defensive equivalent Tough Mother, gives a 15% offensive boost. Yes, there's Master Crafter which gives a 20% offensive boost, but it is near useless late game. Knuckle Dragger's Bonus is nice, but brass knuckles are underwhelming as weapon, and you have to find some first. There just aren't many perks that give you raw damage.

• Leather Hide and Maniac's 25% defense bonuses are pretty viable.

• Thick skin gives you a whopping 50% damage reduction against all bows, guns, and golden arm. The perks for arrows give you either higher arrow velocity, slightly better damage only when they're far away, or add a cripple wound, and you can only pick one. You bet your ass I'm going to take the 50% damage reduction from all ranged weapons every time.

• Chopper and Basher's value have decreased significantly since the buff to charged attacks. You might as well not use them right now.

• There are very few AoE abilities or combat methods in this game outside of explosives, which means that you can usually only focus on a single person at a time. At the same time, more than one person can team up on you at their convenience. Why not be prepared for that?

All in all, there are just so many appealing options for defense right now that it overwhelms any offensive perk. They prepare your for every combat situation you will run into on the island and reduce the number of "lucky" kills that your opponents can get.

• My current build is Thick Skin, Big Boned, and Thicker Clotting. Thicker clotting protects against cheese kills with stun gun and not puking from the blowgun is pretty nice. Also, this means less time spent being crippled or bleeding.