The result is that everybody disables data whenever they cross the border.
So they make practically nothing on it anyway...
Well, practically everybody. Some acquaintances of mine have had ridiculous phone bills after enabling data roaming for an "emergency"... ridiculous on the order of > €1,000 for less than an hour's usage.
It's enough to make me wonder: why don't they lower their prices, so more people would be willing to utilize data roaming? Couldn't they actually make more profit that way? I suppose studies on that subject have already been conducted, and the results doom all of us to suffer on account of a few suckers/idiots: perhaps the same ones that are responsible for spam, due to responding to unsolicited commercial email.
Off-topic, out of curiosity, are you in France, Netherlands, or Germany?