Why does the presence of inna not by itself prove tadhyīl?

Iṭnāb: Tadhyīl, Takmīl (Iḥtirās), and Tatmīm

• Because inna is not an Arabic particle
• Because tadhyīl only allows verbal clauses
• Because every nondeclarative clause rhymes
• Because the second clause must also reinforce the first in meaning