I looked this up sometime ago (my nephew asked me about it after I took him to TLM for his first time). Can’t remember where I found it, but the answer was that if it were not done, the chasible would pull up on the sleeves of the vestment underneath and expose the bare arms of the priest - and that was thought to be immodest at Mass and in the presence of the Eucharist.
Not so much that they were “heavily laden with ornaments” as it had to do with the material and the way they were cut.
So the answer - the action symbolizes modesty and reverence for Our Lord.
Peace in Christ,
DustinsDad