TBF, that was the "most humane" way they seemed to be able to think of, back then. Not excusing any of it in the slightest. Just let that sit for a minute, is all.
At that moment in time, a sufficient number of people aware of this standard were ok with said bullshit —despite everything about it screaming no-effort Americana-brand snow-job (or simply couldn't be arsed to GAF, sure).
FWIW: Edison filmed a fucking documentary of Topsy's 1903 electrocution, the absolute psychopath. 😱🤮😭🤮🤬
(CW: animal abuse, murder, etc. Please be aware that it is gut-wrenching, and will likely stick with you. Proceed at your discretion.)