The adding of depth to what already stands — more meaning laid into existing ground, never replacing it.
Old French enrichir, en- plus riche (rich), of Frankish origin; the noun for the act of deepening.
Its own root travelled to get here: riche came into French from Frankish before it ever reached English, one language enriching another without erasing what was already spoken. Enrichment still works that way — what arrives adds to the ground, and the ground stays exactly what it was.