How do Achievements Work? (The interrelationship between platform, gaming companies, and their consumers)

[Megiddo]

Good day! I'm wondering if anyone might have some solid information in how getting achievements for a platform normally works. Steam seems to go about this better than many other platforms, but consumers here are still often left hanging for achievements that are made readily available for other platforms. I wouldn't think that much effort would be involved here, but I'm curious as to what the main hang ups are. Does it boil down to platforms not asking companies to offer them for their consumers? Are there contracts made where platforms demand that companies only offer achievements for their own consumers? Are consumers able to do much on their end to see more support here?