Written characters and sounds don't usually correspond because pronunciation drifts very quickly in time (even two consecutive generations might have noticeably different pronunciation), and in different directions in different locations, while rules of "proper writing" change rarely, usually as a result of people agreeing to change them in order to catch up to an apparent accumulated drift of pronunciation.
As I understand (in a simplified way), every once in a while (once in a few centuries) there's a major language reform to make written form reflect current pronunciation as much as possible, but already in 100—200 years people would start asking "why do we write not like we pronounce", until some political movement decides reforming orthography would promote their agenda. Then the cycle continues.
Some languages do it way more frequently. Take my native Portuguese. Brazil had 3 ortographic reforms in the 20th century, while Portugal had 5 in the same period, all before the "Ortographic Accord" of 1990, that unified ortography in both countries.
> Written characters and sounds don't usually correspond because pronunciation drifts very quickly in time
In space as well. Local accents can be quite variable. This alone dooms any “we should write words as we pronounce them” to fail unless every region has its own orthographic rules, which would be honestly terrible.
Phonemic / morphological spelling is a thing (or rather a range of things). E.g. Belarusian is spelled phonetically, but Russian spelling is closer to phonemic—while the Belarusian standard could be used to spell the Moscow variety of Russian pretty painlessly, for those of Vologda or Ryazan it would be a downgrade. (This does not stop standardized textbooks or tests from only touching on spelling mistakes that are natural in Moscow, but that’s another story.)
As I understand (in a simplified way), every once in a while (once in a few centuries) there's a major language reform to make written form reflect current pronunciation as much as possible, but already in 100—200 years people would start asking "why do we write not like we pronounce", until some political movement decides reforming orthography would promote their agenda. Then the cycle continues.