The motor itself is a moving part that is subject to wear and tear and reliability and parts availability problems. Solar manufacturers and retailers are notoriously short lived and fragile (in terms of being able to survive changing conditions, like Chinese subsidies, price dumping, and now tariffs, not to mention technological improvements in module efficiency).
If you buy a bunch of commodity modules (panels) without moving parts, you generally don't have to maintain anything except maybe replace the inverters in a couple decades. And you can do that with any electrically compatible parts.
If you have a moving motor, suddenly you need to find all the specific parts for that particular motor, and hire a specialist crew to maintain and replace it, requiring a team with not just electrical knowhow but motor mechanics too.
That's largely incompatible with the US model of solar deployment we have now, which is largely "install and forget" using whatever equipment is currently cheap and available. It's very likely that the equipment manufacturer won't be around in a few years, and that installation company probably won't be for much longer. So any additional possible failure mode should be avoided.
At commercial or utility scale it might be different, but generally it's still more cost effective over time to just buy more modules to offset the less than optimal facing than to try to actively adjust their direction with moving parts. Modules keep getting cheaper. Motors, and more importantly, shipping and labor don't. Installing an overcapacity upfront is still cheaper than maintaining the trackers later.