Didn't the Spanish show up briefly, then come back in force later?
I've heard some speculate that this introduced European diseases, and unlike many Native American tribes, the Mayans lived in dense cities. Such disease would spread like wildfire.
(Certainly, some disease made it the other way too! Tuberculosis and syphilis are examples)
I've heard numbers like 95% died, and it was decades between first contact and serious conquest.
That leaves a lot of time for people to grow up with no one to teach them trades, or even how to read.
If we lost 95% of our population, so many active skills would be lost.
> Didn't the Spanish show up briefly, then come back in force later?
The end of the Incan empire is a really striking example of this dynamic. The Spanish landed on the South American mainland in ~1524, European diseases started spreading, and in 1527 the Incan emperor died from one of the diseases without an heir. This triggered a really brutal civil war of succession that weakened the empire. The Spanish started the conquest proper of the Incan empire in ~1532 and were successful in part because how weak the empire was after the civil war.
So essentially, by arriving early and (inadvertently) initiating the disease epidemics, the Spanish put in place conditions that made the conquest possible a few years later.
Estimates vary wildly on what percentage of the natives died from european diseases. There's just too little information on pre-Columbian populations.
For comparison, estimates of the deaths from the Black Plague in Europe are 30% to 60%. It's a huge error bar, despite having a lot of written records that survived.
The collapse of classical Maya civilization predated the arrival of the Spanish by around six centuries.