1. Feature creep. Unicode was about providing a standardised way to encode text, so you don't get rubbish when mixing writing systems. It wasn't to provide an infinite amount of little pictures of eggplants and the likes.

2. Inconsistent across implementations. It was obvious corporations would use the standard as toilet paper, and come up with their own "unique" interpretations of the emojis, for the sake of "brand identity". Like this:

Not a big deal when encoding actual text, as graphemes are abstract units. Except emojis are primarily used as icons, not as graphemes - their assigned value depends on the icon itself.

3. Obnoxious, distracting, and vague. They're colourful icons in otherwise monochromatic text, of course the reader's attention beelines towards the emoji. I'm not opposed to mindful usage so I'm not automatically blaming everyone who uses emojis, but let's be frank, 90% of the time you find an emoji "in the wild", it boils down to "I'm braindead trash and I have nothing to say lol, but I feel entitled to attention lmao."