If you read the article, experts say that the statistic is rather due to the extremely high amount of red tape required to even file a claim (you basically
need a lawyer). Plus, the idea of paying a niche lawyer for less than 6% chance of success is enough to make everyone give up, and not everyone can afford said lawyer because it is so complex. You also must provide a medical basis and explanation for how it happened (otherwise it's legally just a coincidence), which requires additional paperwork by doctors, hospitals, and so on. And last, all claims must be filed within 1 year
of the vaccination, so if you develop something, say, 10 months later, you have only 2 months to figure out the mess
and file the claim. If it took you 3 months to put the medical basis together - too late.
Plus, it's just common sense. Even by the official statistic of Thrombosis happening in "4 cases per one million" according to the CDC (as one potential side effect), that would indicate we should have 896 cases at a minimum, let alone authorized payouts.