On OpenStreetMap's main site (like here), there are 6 different layer options to choose from (like Standard, Transport Map, Cycle OSM, etc):
However, on OSM's wiki on Tile Servers, not all of these layers are available! For example Transport layer is not available.
Doesn't OSM website itself use a tile server to fetch the tiles corresponding to its supported tiles? Where can I find the tile servers for all of these featured layers?