There is a reason - DCI (the entity that sanctions organized play of Magic: The Gathering) requires genuine, WoTC produced cards. So if you care about playing competitively with the DCI then you need to buy real cards.

But you're always at a disadvantage against someone with a lot of money to spend on genuine cards.

Allowing anyone to use counterfeits tends to level the playing field: just print the cards you want yourself (or buy them cheap, hopefully not at the same price as the real deal!). This also means M:tG turns into something more about skill ("I know how to build an effective deck and play well with it") than about money. I know which game I'd want to play ;)

You’ll always be at a disadvantage if you’re trying to play competitive constructed without a budget. But that’s not what most MTG gameplay is. I agree constructed staples are priced too highly, but most gameplay is friendly matches, and drafting, where the game tends to be more about fun than either skill or money. You’re also forgetting one element of skill that isn’t always restricted by money, brewing. A budget swans deck has won a tournament.

Doesn't that just transfer the disadvantage to your buying power?