There are two different meanings of 'central' in play here, 'center' as in a town square, and 'center' as in the centralized component of a system.
It does not imply that there is a central repository when using 'central' to mean 'a unique, difficult to replicate, or otherwise somehow special component in a system' as in 'centralization'.
Central in the case of 'Maven Central' means something closer to 'default' or 'town square' or such.
Saying that 'maven central' implies maven isn't decentralized would be the same as saying "Most go projects are on github, so go can't be hosted in a decentralized way because github is 'golang central'".
