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The article suggests they do arbitrage.

They blamed their failure on "increased competition for arbitrage opportunities." Properly, arbitrage is low risk exploitation of differences between two markets in the same thing. Cryptocurrencies used to look like they had arbitrage opportunities, with differing prices between exchanges. Mostly, that was because it was so hard to pry cash out of the underfinanced cryptocurrency exchanges. They always had some excuse for delaying paying out. Arbitrage requires the ability to move cash quickly from one exchange to another.

As that situation improved, the spreads between exchanges narrowed. Opportunities for low-risk arbitrage disappeared. These traders reacted to this by going into higher-risk forms of trading. Which is about typical for traders. It didn't end well.