This whole Call Giving Business is not without a healthy dose of irony.
On one hand a trader, the one who receives the calls, is required to understand that to be profitable he must take all the calls. Cannot skip any. But, 99% of the times, after 4 to 5 back to back losing trades the trader skips a few of the recommended calls/trades as a result of his own analysis. This ruins everything.
On the other hand, if the trader is able to completely understand this then he is already at a fairly high-level of advancement as a trader and hence won't need any call service!
And to answer why a profitable trader sell his calls:
If one is genuinely a good analyst-cum-trader and has a reliable structure to profit from, then he could sell it as well. Because the concept of saturation does not apply here. In fact its the opposite. If there are more people participating in a breakout it will be even bigger! And then the skill lies in taking profits.