Yes, they lose 79% of the fees used to do this but overall it might work out in their favor.
They would be giving their money away to other miners thus decreasing their relative hashrate in a downward toilet bowl spiral for themselves. Illogical.
No, spam fees are minimal or even 0. Regular users have to exceed those fees to fit into a limited 1MB block. F2pool wins blocks 21%of the time. Depending on how high they can drive up these fees compared to the minimal spam fees they lose 79% of the time, it could be profitable.
Your mistake is you assume 21% is a constant, but as they drive up fees and giving 79% of the increase away, they drive up the relative resources of the other miners thus driving down their 21% in a spiral. Even if they increase their profitability, it isn't sustainable.