If that were the case paid services wouldn't be doing it too. The reason they do is that there is no large enough incentive/consequence to make a convincing argument to leave that revenue on the table. It is neither hosting it elsewhere nor the "free" services which tend to be the worst examples of it, but rather the lack of any financially valid reason not to.

My issues is it is that data 'elsewhere' bit that they want. Even when I pay they want to harvest my data. Most of the time it is to do the opposite of what the main article is talking about.