In broad terms, the "high-risk" label has nothing to do with a company’s risk of failure. This particular brand of risk analysis looks mostly into fraud and chargeback potential. So, merchants are most likely to get labeled as high-risk if they do business in industries that are notoriously plagued by high chargeback ratios.
Payment processors usually apply a rolling reserve on every high-risk merchant account. This reserve can be used by the acquiring bank to offset chargebacks. The reserve grants an additional layer of protection against unexpected behaviors on the merchant’s website.