The early machine made marbles were competing with the earlier handmade marbles.
The “agate” name that many marbles from the machine made era had was just a marketing thing trying to compete with the old era marbles that were actually agate/stone/clay.
MFC, CAC, Peltier, Akro and others tried to copy what was once popular from overseas in the stone made or hand-mades and they succeeded.
This is my best thought for an answer---
Marble—On!!