You didn't name the exchange youryou're using, not all people have access or are registered to a fiat exchange with enough liquidity allowing to sell large bags at a good price. And in the other way it's even harder not many exchanges will accept large fiat deposits above $50k or 100k in one time without askingrequiring long extra KYC if they accept them at all. In addition I assume if something is wrong with the recipient bank an OTC service will be far more reactive to resolve the issue and give documents than a customer support from a random exchange.

You didn't name the exchange your using, not all people have access or are registered to fiat exchange with enough liquidity allowing to sell large bags at a good price. And in the other way it's even harder not many exchanges will accept large deposits above $50k or 100k in one time without asking long extra KYC if they accept them at all