There is a reason as to why the first cause must have to be uncaused. We can find this reason from our concept of The Whole.
The concept of The Whole is an exceptionally extraordinary concept because this concept not only gives us the evidence that there is a God but at the same time it also gives us the reason why that God must be uncaused.
We define The Whole in this way: The Whole is that which contains within itself everything that exists. As per this definition, nothing can ever exist outside The Whole, because whatever will ever exist, will always exist within The Whole. This is as per the definition of The Whole. So by definition, The Whole will always be spaceless and timeless. So, as per the definition, nothing can exist outside The Whole, because if anything at all exists outside it, then it will no longer remain The Whole.
So far, we have only given the definition of The Whole, but we have not stated anything about whether it exists or not. Let us now suppose that it exists as well. If it exists, then the most relevant question that can be asked will be this: Is it caused or is it uncaused? If it is caused, then who, or what has caused its existence? If it is caused then where lies that cause? If we say that this cause lies outside The Whole, then it will no longer remain The Whole. So, for The Whole to always remain The Whole, its cause must also lie within itself. For The Whole to always remain The Whole, it must be self-caused, uncaused.
So, the definition of The Wole itself gives us the reason why it must be uncaused.
We will arrive at the same conclusion if we now consider the infinite regress problem. In the article ‘Existence of anything ultimately points to God’1 I have already shown that if anything exists at all, that even if a single speck of dust exists, then ultimately there will have to be something spaceless and timeless in nature, as otherwise there will be an infinite regress. We will call this spaceless and timeless entity that stops the infinite regress The Ultimate Reality or The First Cause.
Now the question is: Is this First Cause caused? Or, is it uncaused? If we say that it is caused and that its cause lies outside it, then we will be again introducing the same infinite regress that we are striving so hard to stop. So, if we want to genuinely stop the infinite regress forever, then just like The Whole, this First Cause, or this Ultimate Reality, must also have to be self-caused, uncaused.
Reference:
1. https://www.scigod.com/index.php/sgj/article/view/498/536