You seem to be implying that the El Salvador project of brutal mass incarceration without spending too much effort checking that the incarcerated really are guilty could solve this problem too.

Firstly, it probably wouldn't because that program only began a long time after the majority of the improvement had already happened: https://substackcdn.com/image/fetch/w_848,c_limit,f_webp,q_a... Bukele only began the mass incarceration after El Salvador had roughly the same number of homicides per person as the USA.

Secondly even if it really had been that program that produced the improvements, the gangs in El Salvador were very different to the gangs in Mexico. I found https://mattlakeman.org/2024/03/30/notes-on-el-salvador/ interesting for background on the gangs.

In El Salvador the army/police were better equipped enough to lock up the gangs; in Mexico it's not clear whether the army is powerful enough to defeat the cartels even if it seriously tried to.

Silence, magat