That's not actually true.
No company I know of has ever used a Waterfall methodology in software development. All software development has always been Agile in some form or another, even before the original manifesto.
The Waterfall method originated from manufacturing where each step is defined and changing the design half way through is prohibitive.
I’ll quote Wikipedia here:
The first formal description of the waterfall model is often cited as a 1970 article by Winston W. Royce, although Royce did not use the term "waterfall" in that article. Royce presented this model as an example of a flawed, non-working model.
So get that – There never was a software development methodology called "Waterfall", it’s a manufacturing and construction process used in an article in 1970 to show how it couldn't work with software.