My best answer is...Youtube blew up. The market for it went through the roof, anyone's posting videos all over the internet, and obviously the trolls weren't using their patent to make money themselves, they were using it to ride on the backs of the real developers.
Your best answer doesn't hold water. YouTube was started in 2005, which means it was founded after the first round of these lawsuits had started. These patents are about live content, Youtube was about stored content.
I didn't read up on the patent, and you are mostly right with regards to credit card processing and video chat, but streaming media isn't always live. Were there quite as many of these lawsuits in the first round?
Honestly, the porn industry was always making large sums of money in this type of field, so perhaps Youtube was a little short-sighted. For a more general statement, they started the lawsuits when it became economically viable to, i.e. the companies using the "infringing" patented methods made enough money to sue for / strike a license deal.
