[4cao]

Because it's part of the cultural heritage. Very much like the weird spelling of many English words is.

In particular, the phonetics of Mandarin Chinese underwent several waves of simplification to the point that many characters are pronounced pretty much the same - in particular, there are a lot of syllables pronounced /yi/ or /shi/.

So, transition to a purely alphabetic writing system would mean losing access to all the sophisticated texts of culture. There is even a poem illustrating that phenomenon, and taking it to the extreme: https://en.wikipedia.org/wiki/Lion-Eating_Poet_in_the_Stone_...

More practically, everyone learns their first language as a child, and at that point does not get to decide whether something is too "crazy" to learn or not, since nobody asks their opinion.

Further simplification was attempted at some point by the Communists (also as a means to increase adult literacy) but they rolled it back quickly.

Also, it's not 20,000 "icons" to learn. There are a couple of hundred composing elements ("radicals," although it's not entirely correct to call all of them this), which just repeat themselves in different arrangements, and there are some rules to it. Beyond these, only a hundred or so characters have purely unique elements.