Ask HN: Why is the universe depicted as a cone?

Given this links to a Penrose’s Hawking Points based diagram [1], i am constantly wondering why the universe - or its history is always depicted as a cone.

It’s hard to get my head around it since if there was a big bang, you’d expect a spherical visualization.

I am aware of WMAP and even if the reality is a, b or c - it all goes back to the theory of a flat universe, thus space time.

Since everything we see - on earth and through instruments in space - has three dimensions it is hard to understand gravity by showing a warped plane by spheres.

That works when showing the earth and its moon but is hard to follow once you add a galaxy, a cluster, etc…

Does anyone know of any good explanations and above all visual models that might make this more comprehensible?

Cheers and thanks!

[1] https://physicsworld.com/a/inside-penroses-universe/

Edit: Formatting.