Ah, the usual emoji thread.
Q: Why is Apple adding more emoji?
A: Because emoji are a driving factor in getting people to install updates. That's critical especially for updates that also contain security patches.
Q: No seriously, why?
A: Because a new version of Unicode has more available. While Apple is also part of the process deciding which future emoji make it into the standard, they have to agree with the results, just like everyone else. Otherwise, you end up in a situation where Android or Samsung or Windows have emoji that don't render on Apple's OSes, which people will rightfully blame Apple for (and possibly consider it an argument to move to a different OS).
Q: Their software quality has been going downhill.
A: That's not a question.
Q: OK. Shouldn't they invest resources into improving software rather than adding emoji?
A: It's not an either-or proposition. Adding emoji is largely graphics designer work; most of the software engineering (such as a picker for different skin tones) has already been done years ago. So, adding emoji doesn't take up many software engineering resources, and even if it did, Apple has thousands of other software engineers spread around numerous teams. Make the argument that Apple should focus less on features and more on quality, not the argument that in order to do so, they should stop adding emoji.
Q: But emoji are stupid!
A: Also not a question, but a valid opinion. Millions upon millions of people love them, though, and if you don't, they're really not particularly in your way. Not everything Apple does is about you.