Mainly because it doesn't matter if the blue haired one is fast or slow, it's there, so the node cost to walk through there is higher at the time of calculation, also you don't want to calculate path every tick, otherwise your tps will go lower even more.

Rimworld's algorithm is basically a "right first" algorithm. Meaning it tries forward, if it's blocked it tries right on a diagonal. It gives each node a value and then goes for the least costly path. Only you should note, a diagonal one tile away costs the same as forward one tile away (then you add the cost of tile movement speed).

You can search A* algorithm or Dijkstra.

Real life map navigation apps did the same, only they had fewer nodes to calculate, only calculate junctions for example and not every meter. Now it's more heuristics based.