You are correct that Trichlor is considered a hazardous material so would normally require special placarding and labeling and requires shipping papers which would increase shipping costs. To avoid this, most manufacturers package in a way to fall under the "limited quantity" exception which requires an inner packaging not to exceed 1 kilogram (2.2 pounds) of chemical and an outer packaging not to exceed gross weight of 30 kilograms (66 pounds) as per Title 49 §173.152(b)(1). So that is why the Trichlor tabs are individually wrapped.

Another reason is to reduce fumes since there is liability from opening up a large bucket of Trichlor which can overcome someone standing over the bucket.