I'm surprised about this as well. Even if they didn't want the overhead of running their own tile server, one of the best parts of the MVT format in my mind is

I'm surprised about this as well. Even if they didn't want the overhead of running their own tile server, one of the best parts of the MVT format in my mind is that one-off tilesets like this layer can trivially be thrown into S3 and served extremely cheaply as well. That removes a ton of the effort they put into circumventing MapBox's limitations and is cheaper to host.