Why was everyone in the early 2000s doing this???

Same photographer is a good guess and possibly true. It's also around the time laptops with webcams became a thing for normies. Before that computers were only at work/school or for nerds. Before smartphones, Apple's "Photo Booth" app especially on iMac (marketed toward students and non-technophiles) was a big thing at that moment because you could take a picture of yourself (essentially a selfie, but via a computer) and then manipulate it with filters (before the mass populace knew what filters were). So whether or not there was the same or any photographer involved, there was a trend of people taking straight-on pics with goofy poses as if they were in a photo booth due to the above.