I think it's a mix of multiple factors that led to where Venezuela is now. I am a stalwart believer in personal freedom and the ability of individuals to live as individuals and self-determine. That, to me, is the essence of American greatness (or at least was).
I don't know all of the reasons it occurred, but Venezuela accumulated a sizable portion of their populace who felt justified in voting for confiscatory government. Letting class warfare and rhetoric fester leads to this. Having an economy that doesn't provide sufficient opportunity for betterment to those lower on the socioeconomic ladder encourages this. Having a left-leaning complicit press encourages this, and accumulating a sizable portion of the populace who have become dependent upon government handouts also encourages this.
This should sound familiar, and then add in the effects of rapid demographic shifts because of legal and illegal immigration and you see why we are in trouble.
Mexico, IMHO, is also ripe for socialist takeover. Pemex, their major source of government funding is facing decreasing petroleum production. They don't provide enough economic opportunity to their own citizens. They have high level political corruption and ‘fat cats’. They can't even police some of their own territories. If I were in the CIA I would be looking at what foreign powers are at work trying to foment this type of unrest in Mexico. You know they are there.
The bottom line is that preservation of freedom requires vigilance, and we aren't impervious to what has happened elsewhere.
Even the most minimal improvements in public health ... clean water ... sewers ... inoculation, etc., lead to immediate massive population growth among the lower classes. Then, there are never enough resources to either find something to do for them, or to support them.
In Latin America, this means an increasing racial division as well, since the upper and middle classes are more "European" than the much faster-breeding lower classes. Although there is much intermarriage in Latin society, which does not have our brand of "race consciousness," racial differences do exist and are exacerbated by massive population growth.
Castro took advantage of this by forcing Cuba's middle and upper classes to self-deport, making Cuba much more of an Afro-Latino country than it had been. Venezuela is undergoing that process right now.