Why was tracking covenant state expensive in Kaspa before KIP20?

Before KIP20 covenant IDs, proving a UTXO belonged to a specific covenant instance required attaching parent and grandparent transactions as witness data inside each new transaction. Witness data is extra proof material bundled with a transaction to establish its validity — the more of it a transaction must carry, the more expensive and complex it becomes to create, propagate, and verify. Without a consensus-level identifier, every step in a covenant's life had to re-prove its entire ancestry. KIP20 eliminates that overhead by having consensus track lineage directly, so individual transactions no longer need to carry that historical burden.