My understanding is that the 'witness discount' was created to make the consolidation of UTXOs, and the batching of transactions cheaper.

Legacy addresses were cheaper to spend than to consolidate, meaning that people wouldn't spend/consolidate their change which would result in UTXO bloat over time.

Segwit (and Segwit addresses) made that cheaper (which was its intention) however a much-later byproduct was that arbitrary data, disguised as witness script, also got the same discount basically 75%.

#1 rule of engineering is that design decisions years later can have unintended effects.