Didn't know the trim levels were not the same in different countries. I did note that some people mentioned they stepped up to the EX Premium trim, but in Canada the base PHEV is an EX Premium.
Given the wide range of climates in the US that's not surprising. If you're in Florida, Arizona, Southern California etc heated seats are probably not a feature you care about so there's no point making them standard for cars sold in those places. Probably half of the USA consists of people who don't really see winter and so it makes sense to make them an option. Kia sold almost 600,000 vehicles in the US last year. If heated seats cost $10 per vehicle (WAG, could be much higher) and half don't want then that's $3 million bucks saved. Plus, you can upcharge the other 300,000 folks for the privilege of having them. Win-win! ?For some reason, heated seats are not standard in Mexico! (not even in the US).
Yup, countries vary widely and many local variables are taken into account to different trim levels, standard features, and how cars are equipped with options.