Emojis have names. When somebody sends a "stop sign", "smiling face" or "jack-o lantern" emoji, I know exactly what they mean. Screen readers can (and do) pronounce these.

When somebody sends a bunch of Ancient Egyptian hieroglyphs mixed in with some mathematical symbols, with a little Katakana on top, I have no idea what they mean. The message may encode some visual meaning due to how the characters look and the visual patterns they form when placed in combination, but its semantic meaning isn't clear, so a non-visual technology cannot interpret and pronounce it properly.

This is a very common issue with "fancy font generators", which were common in certain Twitter communities once upon a time.