Tiles aren't being used yet for driving.
Are you really sure? How do we know that without having a clear look at tesla's driving control logic? My guess would have been that the tiles are being used but their quality is inconsistent. At least that would explain the very inconsistent performance of AP on local roads since 10.4. There are videos out there of AP on very windy roads both driving almost flawlessly and failing completely.
Especially this video right here is very curious. At the linked part in the video the road does a series of 3 90 degree turns, but AP only manages to take one of them in one direction (the driver drives through that stretch of road in both directions) while completely failing the other 5 maneuvers.
This is a bit weird because there are tons of videos out there of the recent AP acing way more difficult turns. So I did some digging and checked out the relevant ADAS tiles (c20d6, c20d7) and lo and behold, the quality of the map tiles at that location is very flaky. On that particular stretch of road neither lane has complete splines and only two of the turns have complete and sensible entries in the "local speeds" fields.
But now what's really interesting: the acceleration and deceleration maneuvers AP does correctly in the video match the data from the tiles. On the other hand, the parts of the video where AP is especially awful seem to be consistently on parts of the road that either have no or very incomplete data in the tiles.
Here's another popular 10.4 video. When looking at the tiles of that respective region (u2ede) it's clear that the data in them is a lot more complete with the whole stretch of road being covered, which in turn might explain why AP seems to do a much better job on a pretty difficult road.
Now granted this is only a sample size of two, but from these two examples alone it's pretty obvious that AP performance seems to fluctuate a lot and how well it does seems to be somewhat related to the quality of the ADAS tiles.