It's simple, in France there is this idea that everyone should contribute to "national solidarity" according to how much they can afford. Internet giant are very rich so they should contribute a lot, and currently there is a sentiment that they don't contribute as much as they should, so this law is simply starting to fix that.
And it's a bit rich that, at the same time the US is unhappy with France france over this, the US is imposing on the French economy via FATCA and FBAR.