This is not accurate. Individual epidemics did not have mortalities even approaching the 90% range. What actually happened were dozens of epidemics over decades or centuries. Moreover, outside the Northeast, Columbian epidemics are closely associated with persistent European contact and colonization.
It should also be noted that human populations are incredibly resilient to epidemics. In the absence of "other things", populations suffering catastrophic virgin soil epidemics will typically rebound to pre-epidemic levels in decades. It's not a sufficient explanation for the centuries-long decline of indigenous American populations. The black death was no less severe and successor epidemics continued throughout Europe in the 15th century, yet we see nothing like the demographic collapse of the Americas post-contact.
More than 90% collapse in Mexico from 1520 to 1580, mostly from three epidemics. Starting from ~22m, 8m (37%) dead from a 1520 smallpox epidemic, 12-15m dead (~80%) from a 1545 cocolitzli epidemic, and another ~2m dead (~50%) from a 1576 cotolitzli epidemic. Mexican population didn't recover to its previous highs until the 20th century.
Isn't that because Europe was able to bounce back while in the Americas, the diseases were immediately followed up by the European colonizers who didn't give them time or space to repopulate?
We have a more recent example in Hawaii. Hawaii was not subjugated by any foreign power until the 1890s. That being said, the Native Hawaiian population pretty much collapsed from a high of 300,000 in 1770 to 20,000 in 1920.
It should also be noted that human populations are incredibly resilient to epidemics. In the absence of "other things", populations suffering catastrophic virgin soil epidemics will typically rebound to pre-epidemic levels in decades. It's not a sufficient explanation for the centuries-long decline of indigenous American populations. The black death was no less severe and successor epidemics continued throughout Europe in the 15th century, yet we see nothing like the demographic collapse of the Americas post-contact.