This comment (https://news.ycombinator.com/item?id=24369239) has mentioned that multiple major companies are being investigated, so maybe the investigation into Google just happens to be further along.
That's a good point, but also, given that "and Facebook and Amazon" are often Trump's next words after "Google," it doesn't do much to convince me that this isn't politically-motivated selective enforcement. (Though, on the other other hand, I'm not sure what big tech companies Trump isn't mad at, so maybe this is a low-selectivity filter.)