Why? Because Lord Shiva is not a historical person who performed a sequence of gymnastic poses. He is a principle —pure consciousness. His "poses" are not physical stretches but that symbolize different states of existence.
Search for "Natya Shastra 108 Karanas PDF" or "Shiva Iconography Guide PDF" on academic platforms like Academia.edu or archive.org. Combine those with a list of the 20 primary forms listed above, and you will have built your own sacred compendium. 108 poses of shiva pdf
Thus, the are originally a set of dynamic dance postures, not static yoga asanas. However, over time, these karanas have been adapted, meditated upon, and woven into advanced yogic practices. not static yoga asanas. However