I honestly like 'POL' ticker better than 'MATIC', and one token being used on both chains, it'll be convenient for the user...
Considering the fact that the Total supply of Matic coins is completely in circulation, I think it may have something to do with the upcoming airdrop from Polygon. Thus Max. supply coins POL can exceed Max. supply Matik, while the difference will be aimed at airdrop from Polygon ZKEVM and encouragement of future validators.