What does “waymarked routes” mean, exactly? And same question for the OP.

Doing OSM editing from Mapillary imagery in various US states, I find that the roads that have roadside signage as “official bike routes”, predate modern safe(r) bike infrastructure. These are often highways that frankly look like death traps: no shoulder, high speed limits. Especially when so many North American long-haul cyclists now are riding “bikepacking” setups, it may be preferable for a router to prioritize quiet agricultural tracks and other unpaved terrain over the supposedly official bike route.

Yeah, waymarked routes in much of the US are an absolute embarrassment. Last time I went cycling in NY State the worst part of the whole route was the official State Bicycle Route. The quiet roads were lovely.

cycle.travel treats routes in the States differently to those in Europe for precisely this reason, and there are some routes which get absolutely zero uplift because many of them are so bad (looking at you, East Coast Greenway).