I've spent some time looking at this. I couldn't figure out why Google Directions API sends you up Hwy 89 instead of Lake Shore Dr when starting from Horseshoe Bend. But if you start at Wahweap and end at Horseshoe Bend, it seems to take Lake Shore Dr, and you should be able to "Ride Reverse" that route to get the same effect.
Though when I was testing that, the white dots eventually stopped loading because their reported lat,lon was too far off the Google Directions path. I made a fix for that in our upcoming build, aiming for this Friday.
As for why you can't turn off Hwy 90 to Wahweap Blvd, there seems to be a connectivity problem with Streetview in that direction. If you approach that intersection from Wahweap Blvd to Hwy 90 it works. Not sure how to fix this yet but glad you reported it.
Though when I was testing that, the white dots eventually stopped loading because their reported lat,lon was too far off the Google Directions path. I made a fix for that in our upcoming build, aiming for this Friday.
As for why you can't turn off Hwy 90 to Wahweap Blvd, there seems to be a connectivity problem with Streetview in that direction. If you approach that intersection from Wahweap Blvd to Hwy 90 it works. Not sure how to fix this yet but glad you reported it.