Why don't more games offer incentives for achievements?

Sorry for the repost, but my original post was deleted due to its title being too vague. So I recently finished and platinumed the Nathan Drake Collection, as well as Horizon Zero Dawn. This morning, when I opened up my email, I was delighted to see an email from Guerilla, giving me access to an exclusive theme for getting all trophies for their game. Don't get me wrong, achievement hunting is fun, but it isn't for everyone. Sure you can brag to your friends who probably won't care much, but other than that, most games offer the platinum trophy/100% Achievement for only self satisfaction. Going back to HZD, I actually felt a feeling of completion and my hard work and hours felt like they actually meant something and I was rewarded with something in return. Not only do I commend Guerilla for such a game, but also putting in a little bit of extra time and effort for fans who adore their game, and giving something back to them. I know a few other games did this, such as bloodborne, but they are VERY few in number. Not only do I think that rewarding players for getting all achievements in a game would show the developers actually care and want to give something back, I actually think putting these incentives in for all games would increase their longevity and player base. For example, battlefield 1 has had an enormous drop in player count, and while this may be due to lack of content, etc, etc, I think that if DICE had put in some extra achievements in the multiplayer such as "revive 20 teammates in a match," or "reach rank 100," with a reward such as exclusive skins for their weapons and vehicles, and maybe a dynamic theme or avatar, more people would be inclined to play the game. This may slightly sound like a rant, but I feel like this would make a huge impact on a lot of games, fans, and developers alike.