I'm relatively un-informed on the history of pre-conquistador cultures and civilizations of the Americas, but i always thought that the human inhabitants of this region migrated to these continents via a land bridge connecting Asia to North America. If that were the case, wouldn't there be more developed ancient civilizations in North America? My basis for this reasoning is that NA would have been settled longer than SA, simply because of the proximity to the land bridge. That being said, there are no ancient ruins in NA that even come close to the scale of what the Aztecs and Mayans left behind. Was curious why this is the case.
Reedstilt's previous posts on this topic are excellent, so I recommend reading his posts. However, your question also makes several assumptions that should be more explicitly approached.
Have there been any explanations or theories as to why Native Americans never progressed to the level of the Ancient Aztecs?
To unpack this, you very clearly have an understanding that although we have evidence from historical societies, we don't have those societies themselves. We interpret surviving evidence in the present that was produced by societies, people, and processes in the past. That highlights part of the nature of the 'theoretical gap' between our interpretations of evidence and whatever reality existed.
However, it's not a straight line from evidence -> interpretation. The fanciest pyramid doesn't tell us anything until we bring in our own theories and assumptions to understand labor organization, specialization, and trade networks.
The above isn't simply theory for the sake of being pedantic, but also because it's crucial to understanding why your question may not be in line with academia to begin with. The relevant words in your question to this point are 'why Native Americans never progressed to the level of...'. You are taking for granted a progression from some level to another level. Not only that, but as you ask later, this progression as a temporal component. If the more Northern regions of NA were settled for longer, they ought to have more socially complex societies.
This is not a bad question by any means, but it brings in teleological assumptions broadly named 'Spencerian' about how societies evolve from simple tribes through various levels of social complexity to the state, the ultimate expression of societies.
That being said, there are no ancient ruins in NA that even come close to the scale of what the Aztecs and Mayans left behind.
Here you introduce another idea, that of 'scale'. Scale can mean many things, including population size, density, 'highest' technological complexity, 'average' technological complexity, size of constructions... etc. There are so many possible facets to any individual human society that picking merely one as a basis for 'scale' comparison can be used to decide answers in any way you favor. For instance, if we were to discuss scale in the context of inhospitable land transformed into workable farmland, the Hohokam of what is now Central Arizona had perhaps the largest irrigation network in the world at the time. At the height of their 'civilization', they inhabited an area roughly the size of Belgium and transformed much of it from arid desert into fertile irrigated fields through diversions of the Salt and Gila rivers. They did all of this without the use of state-like apparatuses which would rank them much lower by other meanings of the word 'scale'.
These are all tricky concepts in detail, despite how easy they are for us to discuss intuitively. It's worth considering just what question you're really asking when you use the words 'scale' or 'progress'.
I dealt with a similar topic in this series of posts. It's in archive mode now, so if you have any follow-up questions, feel free to ask them here.