[epmaybe]

I'm confused about why everyone is surprised that something that elicits an inflammatory response in the body can increase your risk of blood clots. Increased inflammation -> increased clotting in a number of diseases, not limited to coronavirus. A quick literature search reveals that this is the case for a other viruses and autoimmune diseases.

This was a particularly enlightening paragraph from StatPearls: There is an interplay between inflammation and the coagulation system. Inflammation triggers a hypercoagulable state.[45] Endotoxin activates the complement system leading to thrombocytopenia and hypercoagulability.[46] The relation between inflammation and coagulation can be observed clinically in patients with purpura, vasculitis, and septic thromboembolism.[47][48] Coagulation helps to limit the expansion of infection, and some bacteria use fibrinolytic properties to oppose this response. Autoimmune diseases like systemic lupus erythematosus, immune thrombocytopenic purpura, polyarteritis nodosa, polymyositis, dermatomyositis, inflammatory bowel disease, and Behcet's syndrome increase the risk of thrombotic events.[49][50][51] The cytomegaly virus (CMV) has correlations to atherogenesis through a change of the cellular lipid metabolism and leukocyte adherence.[52]

https://www.ncbi.nlm.nih.gov/books/NBK538251/