Well first of all, organized crime does not need an online platform to profit off of fixing professional sports games. There are still plenty of bookies running around offering better odds than draftkings. Though, if they really wanted to, they could make smaller bets under hundreds of accounts.

There is also the very strong possibility that they are colluding with the online betting platforms in some way. Coupled with the fact that any difference-maker athlete is getting a huge salary, and blackmail/extortion becomes your best option to getting one on your side.

Organized crime operations have no problem getting a lot of people involved in their schemes. They wouldn't use one account. They'd spread the bets over a large number of people and accounts and also possibly sell the information.

Yeah, that would limit the scale if they were betting against the platforms.

However, if you assume they were feeding the information to the platforms...

First, people who are banned from online bookies use "horses" or other not-banned players to place bets for them.

Second, the FBI is targeting real world Mafia members, who will typically be the bookies taking action from others. If they know in advance, through blackmail or collusion that an NBA player or coach will throw a game, they can exploit this versus their entire betting pool for massive wins against the suckers placing bets with them.

You're focusing on a game with player vs. house odds, like a casino. Online betting platforms do offer some of these games but they are clearing markets for gambling; they manipualte the odds to arbitrage wagering and take a cut regardless of the outcome. It's all about volume. If you make a huge wager on a long-odds parlay, they no longer look the same for the next (or other side) of that specific (or components of the) wager.

An organization could place the bets through different people each time.

with that level of sophistication I’m sure they’re not using the inside info to place bets on retail platforms.