The hard truth is that sometimes you can't expect to get any praise, gratitude, or even feedback from the OP. In our Q&A format, all that the site really needs is that a question is asked and an answer is given. Everything else is just added bonuses.
An important thing to remember in those circumstances is that your answer is not meant only to help the OP, but to help everybody asking the same question, especially googlers. It may be tough when the OP does not recognize that you put effort into answering, but I can tell you that the rest of us at Physics.SE appreciate you taking the time to be thorough and accurate. And if your answer is decent, take comfort that it will probably be enjoyed by the community and rewarded with upvotes.
We cannot and would not institute a forced feedback system. There is nothing anyone can do to force an asked to give feedback. Regardless what is implemented, it will always be possible for someone to post a question and then never log in to the site again. Furthermore, how can we define what is a decent answer? If someone posts a good question and the first and/or only answer they get is a drive-by crackpot answer, then how can we force them to give feedback when they might just want to ignore it? Or if an answer is really kind of meh but there's no way you know to make it better, what would you force someone to say?
"Hey, thanks for answering but this isn't a great answer and I doubt you can make it better"
No, that would be terrible for so many reasons.
So while the rest of us appreciate and applaud your time and effort in posting the elaborate answers, feedback from the OP is one of those things you can't always expect to get nor can it be forced out of them. Just smile, be happy when you get feedback, and remember that you write such great answers not just for the OP but for the whole community. And some other nonsense about a good deed being its own reward.