Market makers typically have a requirement to be in the market a certain (high) percentage of the time. In return, they get rebates (which can be a significant source of revenue) and protections from the exchange against overfilling. This can help them for certain shock events.

Most likely, though, their profitability % is tuned by edge and risk parameters. They can adjust size, widen out, or tighten up the spread to tune trade frequency and profitability. They are finding a sweet spot between # of trades and profitability.