"developer" is a slightly weird way of putting it. osm.org is the contributor portal and demo site for OpenStreetMap, and yes it is not and never has been intended as an end user replacement for Google Maps and similar offerings.

The main purpose of the maps on the site is, besides showcasing some topical uses of OSM data, rapid feedback to contributors, which is something that required specific development so that can be provided with vector tiles too.

The 'late to the game' narrative seems to be a bit misplaced in any case given that OSM data has powered essentially all vector tile use outside of Google over more than a decade.