One idea!

I think they dont mine with hardware they collect the Bitcoins and make speculation on the bitcoin markets. Maybe with good bots and they have earnings much more as 40% in one month. In this case they can pay over years good earnings and make by themselves good earnings.

Some people earn their money at forex. This people make it with bitcoins. If they are good or have good bots they can do a long time but not for ever that is clear.