This also means I cannot find any old app/game on play store. So even with adb (which I do not think is a good solution because it excludes 99,9% of the users, not only tech-savvy users want or need older apps) I can only install apps I know of and that I can find their apk on the internet. I cannot browse the play store for them. I cannot search for something I need, because I will never find them. And if it is a paid app/game? Well, tough luck, I have to go find a cracked apk in shady marketplaces.... So much so for security.
If they really do this for security, it could have been a switch in the developer settings or anything like that. Not a hard ban on older apps