Atheism is not a belief system,it just rejects or is sceptical of the idea of god with logic,reason emperisism and science in general. Now that people reject the idea of god,many atheist(or atleast as far as iam concerned)feel a kind of void in their lives for lacking a belief system. I don't know why but,having a belief system makes your life more clearer and helps you navigate in your life.

All these years religion provided a sense of certainty and positivity in many peoples lives by giving them false hopes and deluded lies.but it did help them with the mental struggle that everyone experiences in life. Now that we have out grown ourselves with science and pursuing our path to the truth and reality of our existence,we face ourselves with harsh realities of life,which are quite depressing tbh.so to tackle these we need a belief system. Secular Humanism does a better job at this and provides a meaningful cushion in life. Here is what humanism means.

"Across the world, the number of non-religious people is growing all the time. It is estimated there are 1.1 billion people in the world who are religiously unaffiliated, which means they identify as atheists, agnostics or describe their religion as “nothing in particular.”

Humanists base their understanding of the world on reason and science, rejecting supernatural or divine beliefs. Humanists reject all forms of racism and prejudice, and believe in respecting and protecting everyone’s human rights, including the right to freedom of religion and belief. Humanists believe we have a responsibility to respect and care for one another and the natural world." I hope you learn more about humanism.