Because 'beer' is said flat, whereas when you say 'gear' you slightly raise your intonation to say 'ge-ah'
Nope, they're close rhymes the way I say them.
Beerrrr, and
geerrr.
To answer the OP, there'd be so many different spellings it'd be very confusing. My phonetics would have
rs at the ends of words, kyser's wouldn't (except where they don't exist in my accent, like law
r). My spellings would have
hs in why, where, what, whether. Many people's wouldn't. And so on.
The argument for standardised spellings is that we, for example, know what is meant by
they're,
there or
their. A phonetic rendering would create ambiguity. And when I write
whether, you know I don't mean
weather. I pronounce them differently, but some people do not. A standardised system ensures that meaning is maintained however the reader and/or writer would pronounce the words.
That doesn't mean I think there should never be updatings. Just as spoken English evolves, so should written English. Not faddishly, to include the latest catchphrase, such as "whatevvuh", but sensibly, to remove unnecessary archaisms and complications.