You may be thinking "hey, how come I have to wait until November/early 2019 to get Android Pie when Google's Pixel phones have it now?" Well, Sony has an answer.
Sony released a fun little infographic about the work Sony does in order to get Google's Android updates ready for Sony's phones. This includes getting the new Android software onto Sony's system, updating graphics and UI, making sure key functions don't break, and testing it to make sure the whole thing works. It seems like a lot of work, which could be Sony's excuse for making you wait months at a time.