You are assuming that ALL professional traders are SO successful that they can lose 10% of their account one month and be able to afford to take an entire month off the following month. I would have to disagree with that statement, but are there PRO's out there that can chime in on this subject ???
You are not looking at the Trader as a trading BUSINESS.
As a trading business, "revenue" comes from trading profits.
@gaussian mentioned a good portion of the account is used as "cushion."
Most businesses call this "working capital".
From working capital, in my case W2 wages which includes payroll taxes, are paid to me. Once paid, it is mine to do with as I please, at the individual level... just like any working stiff living life on a hamster wheel. In this way, trading profits always go to replenish working capital first, and additional accumulations, again in my case, can be used to expand the trading account or can be distributed to shareholders of the entity, outside of and in addition to W2 wages.
So if a trading account is say 25K... with as example monthly W2 wages and other business expense of say 10K, only 15K would be used for for generating revenue. If working capital somehow got depleted, just like any other business the business either gets re-funded or closes. Not to be overlooked however, is that while the total account value is generally considered fixed, financial engineering can be, and is, employed.
if I lost 100% of the trading portion in one month, I still got paid! If I was a good hamster, I stashed plenty of nuts so I could take a vacay if I wanted. Or start again. Or open a donut shop. Or, and, or, and, or...... I trade futures intraday. I am flat end-of-day, everyday.