https://www.chilango.com/musica/tianguis-musicales-cdmx/

The real reason comes since the day of this kind of tianguis exists before the boom era of internet. some even assure Lacri made a public concert in one of those tianguis before they found a proper place in Mexico for their concerts. Pro-tip a lot tianguis still a thing even in this internet era, recommended to search to those who plan to have fun at Mexico if there's some in the state you plan to do some tourism.