It only really became a standard idea in the 1960s:
As recently as 20 years ago, the Big Bang was one of many ideas that scientists continued to entertain: quasi-steady state theory, plasma cosmology, and quantized redshifts remained mainstays in the scientific literature. But today, it’s largely crackpots and a few fringe contrarians who muster even the flimsiest of challenges to the consensus position: that the Universe began with a hot Big Bang. Is the field of cosmology succumbing to groupthink, as its detractors often claim, or is the lack of alternatives justified? Let’s dive in and find out…
So what happened over the past few decades, that all of the major challenges to the Big Bang have fallen away? Two major events: the collection of large suites of high-quality data, which validated the Big Bang’s major predictions to incredibly high precision, and the fact that the main advocates of the alternatives — once they no longer became defensible on their own merits — got old and died.
If any scientifically viable alternatives to the Big Bang ever arise, almost every modern cosmologist would thoroughly welcome it, and then immediately put it to the test.Ethan Siegel, “Why Isn’t Anyone Seriously Challenging The Big Bang?” at Forbes
Well, not so sure they would put it to anything like a serious test.
The Big Bang has been very unpopular. It reeks of purpose and is an incitement to theism. It survives only because the evidence rules out all alternatives, as Siegel notes.
But don’t mistake frustration on the part of naturalist atheists for acceptance.
This is the kind of thing naturalist atheists hate:
See also: The Big Bang: Put simply,the facts are wrong.