When people look for an emoji in their phone's keyboard to express something, they don't read the Unicode description for that emoji. When people receive them, they don't read the description either.
Thus why it's important that, even if they don't have the same style across platforms (like an 'a' in Helvetica and in Times), they have to depict the same thing.
For example, if from your HTC phone you send a smiley that looks pretty content and calm, users of most other platforms will receive it as "I'm freaking sick of this". The meaning encoded in Unicode for it is "face with look of triumph" ( https://emojipedia.org/face-with-look-of-triumph/ ), which isn't what you meant, nor what your receiver understood.
Thus why it's important that, even if they don't have the same style across platforms (like an 'a' in Helvetica and in Times), they have to depict the same thing.
For example, if from your HTC phone you send a smiley that looks pretty content and calm, users of most other platforms will receive it as "I'm freaking sick of this". The meaning encoded in Unicode for it is "face with look of triumph" ( https://emojipedia.org/face-with-look-of-triumph/ ), which isn't what you meant, nor what your receiver understood.