[crazygringo]

Helvetica (Neue) comes in more weights and variations than practically any other typeface. So it is really a thing.

https://www.myfonts.com/fonts/linotype/neue-helvetica/

Also, Helvetica is popular in large part because of the very precise personality it has with is quite amenable to the image corporations often like to portray. It become widely available on computers, starting with Macs, because it was already such a useful font. Major corporations aren't choosing Helvetica simply because it's a default font on computers. And, of course, it's not like a majority of companies use Helvetica for their branding or anything -- it's a popular font, but where popular means maybe 3% or 5%, not 50%.

[Firehawke]

Another way of saying it would be:

Helvetica was put on Macs because it was so popular as a useful font, rather than it becoming popular because it was on Macs.