Netdecking - Always need wildcards

I've been playing since Beta, and have lots and lots of cards. According to MTGA Assistant, I have 47.8% of cards in Arena.

And yet, when I either use a tool like MTGA Assistant, or just copy/paste decklists...I always need wildcards to complete decks. Even pauper decks from a few years ago.

I can't imagine there aren't *any* decks I can import, but maybe I'm wrong.

Also, I am a 100% casual player, and want to find some decks that are good so I can learn to build better decks.