I am pretty sure it's not true that "no one" claims there was not a singularity at the beginning.

http://www.hawking.org.uk/the-beginning-of-time.html

I even saw that recently Stephen Hawking started theorizing that the "Big Bang" was like a black hole. And other physicists weigh in:

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/...

Look at this wikipedia article. Someone must be writing it?

https://en.m.wikipedia.org/wiki/Initial_singularity

In fact there are some contradictions between Quantum Mechanics and an actual big bang:

https://m.phys.org/news/2015-02-big-quantum-equation-univers...