It doesn't really make a lot of sense to apply lubricant to the seals before putting the car in the showroom. First of all, the roof works just fine on a new car that has never been driven. Second, the cars are shipped from the factory with a protective adhesive sheet material (Rapgard) stuck all over the car, even if a seal was physically missing, water would not get inside. Normally, the dealer does not remove this material until the car is brought inside the showroom - in other words, vehicles that have arrived and are simply being kept in inventory are usually left in the storage compound with the Rapgard (and all the other protective shipping coverings) still in place. Lastly, the lubricant is greasy when it is first applied, and people would get it all over their hands (and all over the paint and upholstery of the new car) if it was applied to the car and the car was then put in an indoor showroom for display.
The whole point of lubricating the seals on the day of delivery is to ensure that everything is all set to go when the customer takes delivery of the car. The same concept applies to other components of the car, for example, the battery is always charged on day of delivery, because it is assumed that it will have depleted somewhat during shipping. It's pointless to charge it prior to day of delivery unless the car doesn't start. Tire pressures are always checked on day of delivery, other fluid levels are always checked on day of delivery, etc. All of these tasks are need to be repeated periodically throughout the life of the vehicle, thus it only makes sense to ensure that the "clock is set to zero", so to speak, on the day that the customer takes delivery. This strategy ensures the highest possible level of customer satisfaction.
I suppose that if VW starts to get complaints from prospective customers (showroom visitors) that roof seals are leaking on cars that are on display in the indoor showrooms, they will take a second look at things and perhaps revisit the issue. But I have not heard of any complaints such as this yet.
About your suggestion that the factory pre-lubricate seals - listen, I know you are very keen about cars, but I honestly don't think either one of us is qualified to start telling the factory how to build cars. Let's just stick to things that we know, in other words, things that we have personal experience with.
PS: Before you raise an objection about "the lubricant is greasy", let me answer it for you. The lubricant is going to stay greasy as long as the car is kept indoors. As soon as you take it outside, drive it around, get some dust on it, wash it once or twice, etc. the surface greasiness will go away.