It's a lot more subtle than that. First off let me say that historically, demonstrating that a virus causes cancer has been a major bit of work, and many times people have mistakenly seen associations and falsely believed they were causal. second, I don't deny there are some cancers which are caused by viruses. But, you're referencing extremely rare cancers, not the cancers that make up the bulk of US (or world) deaths from cancer. My complaint is about taking these relatively rare situations and implying there's some sort of general underlying well-understood cause, when the reality is, in many situations, the virus itself did not specifically "cause" the cancer, but for complex biological reasons, it's "associated" with the cancer (which could manifest as increased susceptibility to getting particular types, or worse prognosis, or even possibly better outcome).