Google Maps is now a business directory with a map interface.
The highest contrast is reserved for business that are paying Google for advertisements, followed by other shops, hotels, restaurants and bars.
Everything else, but especially roads and railways, are desaturated into mush.
Compare Streetmap UK[1], which was the first popular online mapping service for the UK in 1997. The web design has hardly changed, and up to the linked zoom level they're still showing the standard (government-produced Ordnance Survey) "paper" maps.
I'm somewhat sure that the low contrast predates advertisement on maps by several years. I also doubt Google would willingly compromise Maps's usability for the sake of advertising, especially right from the start where there is enough low-hanging fruit and revenue is bound to be negligible. That would be like plastering ads over the google.com homepage, something they continue to resist two decades in.
My money is on either a wish to make (all kinds of) labels stand out, or just aesthetic preferences. FWIW I always found OSM to have too much contrast (and too much details), and the emergence of all these services rebranding OSM in different styles would seem to be evidence for other people also considering OSM's default style to leave room for improvement.
The highest contrast is reserved for business that are paying Google for advertisements, followed by other shops, hotels, restaurants and bars.
Everything else, but especially roads and railways, are desaturated into mush.
Compare Streetmap UK[1], which was the first popular online mapping service for the UK in 1997. The web design has hardly changed, and up to the linked zoom level they're still showing the standard (government-produced Ordnance Survey) "paper" maps.
[1] https://streetmap.co.uk/map.srf?x=531405&y=181525&z=115