jmsbert
I have checked the tagging - currently the roads are classified as "service" ... and indeed routing software like graphhopper [1] prefers these roads over the longer secondary highway. From my understanding the tag "highway=service" is not correct here. Highway=residential is more appropriate here. Let's see if this will change the routing algorithm. Are there any street signs that restrict the traffic (maxspeed, maxweight or no HGV's)?
[1] https://www.openstreetmap.org/directions?engine=graphhopper_car&route=28.4938%2C-17.8435%3B28.4893%2C-17.8316#map=16/28.4966/-17.8346&layers=N 