Just spitballin here. Is the route taking a highway? (I think I see an on ramp). If so, I am about 85% sure the algorithm is just assigning too much value to highways. Generally, highways should be "valued" more to avoid just going down tenthousand sidestreets to get everywhere.
It is probably an old case design. In the early water cooling days, there would be separate watercooling units that sat outside the case. The grommets were so you could pass your tubing through.
I wouldn't really worry about the dust tbh, you will wind up having to clean it regardless.