Why so many symbols are included in the Unicode standard

There aren't that many "characters" you use on a regular basis, not much more than what's on a laptop keyboard, but even then there's probably a few extra. But there's over 100,000 characters in the unicode standard currently.

My question is why they are actually characters, which are mapped to fonts. I don't understand why they are not just "items" that you select from a dropdown like on the iPhone. This way they could be completely customizable and wouldn't be so limited/static. Not even just talking about the completely graphic-esque ones like the animal unicodes. Even things like diacritics could be something from a dropdown rather than a complicated hidden keyboard combo invoking a font glyph.

Basically wondering, from a more UX perspective, what may be the reasoning behind having so many statically defined, yet complicated, font characters, rather than just having them be "icons" broadly, that don't map to key codes.