After all, if your gain from supporting IE6 is higher than the cost of supporting it, it makes no sense to abandon IE6.
Although is you abandon full support in IE6 and users want to stay and so use another browser then you've kept their continued custom and saved your extra dev costs. That is, it's not a given that removing full support will impact your profit.
Also, the improved design that could be purchased with the extra dev costs could net you more customers using a browser made less than 8 years ago or indeed convert more of the same.
People can have a non-profit motive too.
The less savvy users are the more likely they are to click on ads in my experience