I didn't see the appeal of remote start until I received a company car with the factory equipped option. It really comes in handy for those mornings when time is tight and the windows are frosted over. I've put over 100K miles on this car and it has not malfunctioned once. My new car comes in next week and remote start was not available through the fleet company. Guess I'll have to put one in myself or get a new ice scraper.
My concern about an aftermarket unit would be whether or not it will activate the rear defroster. Not all do. Without that, it would be of significantly reduced value to me.
So, why do the Japanese not offer them as commonly as other manufacturers? I'm not sure if that's true but let's assume that it is. There could be a number of reasons. I would guess that at least part of it is that dealers are not ordering cars with it. If there is a dealer installed option, the incentive would be for the dealer to order cars without it to make additional money putting it in when you buy the car.
Also, dealers order the cars they think will sell best. Years ago, I tried to buy a new Volvo 850 with a manual transmission. No dealer could find one in inventory in the entire state with a manual. It was a legitimate option, but no dealer had one in inventory because they were afraid that no one would want it and it would sit for months. I could order one, but there was no way to test drive it ahead of time. I chose a 5-speed Maxima instead. I don't blame Volvo for that, it is simply a reality of the American market.
If the car is built overseas it can improve logistics immensely to reduce the number of variations available. This is especially important for the smaller manufacturers like Subaru.
Perhaps their marketing has indicated that the target demographic does not represent high demand for this option.
There could be dozens of reasons or you could just be wrong entirely. Since I doubt there are many Japanese car company executives on this board, what kind of answer did you expect?
