I think that it would be beneficial to first define “religion” and be clear on the meaning before an answer to the question of “Is there any reason, any religion should still exist?” can be found.
As a starting point, the definition of religion, per Merriam-Webster, can be: as an organized system of beliefs, ceremonies, and rules used to worship a god or a group of gods.
Based on this definition with the belief in gods, it may be simple to answer the question by making an argument that gods do not exist and therefore the belief in gods is not rational and since religion stems from a belief in gods, religion is not rational and therefore there is no reason any religion should still exist.
However, it has been theorized that religion arose out of a human need to understand the world in which we live. Religion provided, and provides, explanations for those things that humans did and do not understand e.g. thunder is the noise that Thor’s chariot makes as he rides into battle and a person goes to paradise after death if they accept Jesus. If you accept the religious beliefs then you have your understanding thus fulfilling your need and the world became a less confusing and therefore better (maybe) place to live.
Based on this, the definition of religion may need to be expanded to something like: religion is the acceptance of something as existing, as true, and/or as correct without the ability to prove and/or explain why or how the something exists, is true, and/or is correct. Or in other words: religion is a faith in something.
If this is the case, then it becomes much more difficult to answer the question of whether there is any reason any religion should still exist. If religion provides people with an understanding of the world that they desire/need, then it could be argued that that is a reason that religion should exist.
Now some might argue at this point that there is no reason that any religion should exist because science and philosophy can provide an understanding of the world without faith. However, I do not think that this is the case and I think that religion, based on the expanded definition, does and should exist.
Based on the expanded definition of religion, faith in anything is a religion and anyone can follow that religion. There does not have to be a deity, or rituals, or places of worship, in order to have faith. All that is required is that one cannot prove or explain an understating of that which they consider to be true and/or correct.
The reason I think there is a need for religion is because the bulk of human knowledge, either an individual’s knowledge or the collective knowledge of the human race, is built on steps, that is one piece of knowledge is built upon another or: A leads to B which leads to C which leads to D. I recognize that the accumulation of knowledge is not always linear, e.g. the knowledge of how to build a fire came before the knowledge of the chemical process of fire, but, in general, it appears that knowledge is built on steps.
So at this point, it appears that religion, based on the expanded definition, is all around us and many, if not all, people practice religion in one form or another. You may understand and be able to explain everything about D and know that D is true and correct based on your experiences or whatever, but if you do not also understand and cannot explain everything about C, B, and A, then what you have is faith that C, B, and A are correct, and therefore you follow a religion.
Now there is not necessarily anything wrong with this. It is possible that due to lack of time, or motivation, or intellectual capacity, or some other reason, you are not able to understand or explain everything about C, B, A. This does not necessarily mean that D is not correct or true, rather it just means that you have, and need, faith in C, B, and A. For example, I know from personal experience that if my car is running properly it will get me down the road, this would be D. I do not know and cannot explain the mechanics and physics and everything else about why my car get me down road, that is C, B, and A. So I have faith that C, B, and A are true and correct therefore follow a religion.
So back to the question of is there any reason any religion should still exist. If we accept the expanded definition of religion above, then the answer is yes. Religion needs to exist because you, the individual, with all of the limitations of a human, finite time, finite energy, etc., has and needs to have faith in things and therefore you have religion.
Of course, another definition of religion could produce an entirely different answer.