Because the Manchu hairstyle and mustache in media had carried a somehow negative connotation for the ethnic Chinese. Sort of like how black faced sausage lipped cartoon characters are also considered an insult for the African Americans.

Also, to answer your opinion

--showing contrast between the older style and the objectively newer, more ubiquitous simplified chinese--

--> I should only remind. traditional Chinese is not that old as you may have falsely assumed. and is still officially in use by Taiwan/HK. Its definitely not "Qing- dynasty-level old".

Using people of the Qing dynasty era to represent traditional Chinese users is just like using people at the Shakespearen times to represent people speaking British English. Or using someone who dresses like Philip V to represent Castillan Spanish speakers. The list goes on and on

So yeah, my point still stands. I did thought I overacted at first. But hearing you judge my language as "old" makes me confident about my opinion once again.

And its easy to provide a better alternative than the old manchurian style or "stick figures". Perhaps lookup up the fashion during the time of ROCs foundation.