It's complicated. So this mainly boils down to the relationship between UTC and ESC.
ESC contributes to UTC, along with other groups (e.g. Scripts Ad Hoc Group or IRG) or other individuals (you can submit documents to UTC [1]), and technically UTC has a right to reject ESC contributions. In reality however ESC manages a huge volume of emoji proposals to UTC and distills them down to a packaged submission, so UTC rarely outright rejects ESC contributions. After all ESC is a part of UTC so there is a huge overlap anyway (e.g. Mark Davis is the Unicode Consortium and ESC chair). "UTC rejected" emojis thus generally come from the direct proposal to UTC.
You can see a list of emoji requests [2] but it lacks much information. This lack of transparency in the ESC process is well known and was most directly criticized by contributing experts in 2017 [3]. ESC responded [4] that there are so many flawed proposals (with no regards to the submission criteria [5]) that it is infeasible to document all of them. IMHO it's not a very satisfactory answer, but still understandable.
ESC contributes to UTC, along with other groups (e.g. Scripts Ad Hoc Group or IRG) or other individuals (you can submit documents to UTC [1]), and technically UTC has a right to reject ESC contributions. In reality however ESC manages a huge volume of emoji proposals to UTC and distills them down to a packaged submission, so UTC rarely outright rejects ESC contributions. After all ESC is a part of UTC so there is a huge overlap anyway (e.g. Mark Davis is the Unicode Consortium and ESC chair). "UTC rejected" emojis thus generally come from the direct proposal to UTC.
You can see a list of emoji requests [2] but it lacks much information. This lack of transparency in the ESC process is well known and was most directly criticized by contributing experts in 2017 [3]. ESC responded [4] that there are so many flawed proposals (with no regards to the submission criteria [5]) that it is infeasible to document all of them. IMHO it's not a very satisfactory answer, but still understandable.
[1] https://www.unicode.org/L2/
[2] https://www.unicode.org/emoji/emoji-requests.html
[3] https://www.unicode.org/L2/L2017/17147-emoji-subcommittee.pd...
[4] https://www.unicode.org/L2/L2017/17192-response-cmts.pdf
[5] https://www.unicode.org/emoji/proposals.html