This bike is a fairly capable machine that will drag you slowly to just about anywhere you want to go without much fuss. It is extremely simple, low maintenance, gets great gas mileage, has amazing aftermarket support, and will take a beating without breaking a sweat. If your intended riding aligns with this it will feel like a fantastic jack of all trades not even close to master of anything. If your intended riding does not align the jack of all trades bike will quickly become the not good at anything bike.
On top of that it is a very approachable first motorcycle for a lot of reasons. It has a low seat height, step-through frame, no (real) clutch work, and fairly low price. Many first time or newer riders will pick up a Trail with an idea of what their preferred riding will be, and quickly figure out that what they actually like to do is completely different from the idea they had in their head. Maybe they think that they'll only ever do light trails, and then find that they want to do more serious off-roading or single track riding, and so outgrow the capabilities of the Trail. Maybe they think they want to keep it local and won't need much top end, and then find out they want to go further than they thought and find themselves holding up traffic in an uphill 50MPH zone and so outgrow the capabilities of the Trail.
The Trail is a fantastic little bike, but it does fill a very specific riding niche that not as many people fit into as they might think. The approachability of the bike, and the fairly low price make it easy to pull the trigger even if you're not 100% sure you align with the bikes capabilities. This combined with the fact that you'll likely never see one, let alone sit on one, beforehand makes it difficult to actually know whether the bike is right for you before you buy it. Predictably, this leads to more instances of people buying the bike and realizing it's not exactly what they are looking for.