Non-witness data (L0) is immutable objectivity. Witness data (L1) is subjective and necessarily optional per SegWit soft fork.
Fees are low because L1 expanded blockspace beyond the 1MB definition to up to 4MB by using arbitrary discounting of the same physical bits stored by nodes. This pushed fees away from L0 blockspace paid in sats to fees paid in bits as L1 segwit data, since segwit bits cost 1/4 price in sats, but are the same physical bit on nodes.
