The people who were pushing the fact that you'd have sole control over your wallet were those who wanted to be immune from the government seizing their money: s

The people who were pushing the fact that you'd have sole control over your wallet were those who wanted to be immune from the government seizing their money: scammers, criminals, tax dodgers, and exchange runners (a combination of the first three). Those people put a bunch of money into bitcoin to inflate the price, but they need a bunch of rubes trading the currency to keep the value of the coin (relatively) stable so they can withdraw their holdings, but they don't care much if those rubes have full control, and that's where exchanges come in. Exchanges are there as a way for the first movers and the ultra-wealthy to extract wealth from uninformed, naive new investors into crypto.