During the Swiss movement, there was a need to unify different cultures due to the rise of globalism. The movement led to Helvetica and its universal appeal.

Helvetica's ubiquity allows it to fade into the background while giving a message to a diverse audience. However, it is often unnoticed and underestimated. It is this invisibility that makes it so appealing and so integrated as a typeface. “Helvetica maybe says everything, and that's perhaps part of its appeal—it is almost INVISIBLE” (Jonathan Hoefler).

theory #2:

UNIVERSALITY

Universality Image 1

A sign in Amsterdam uses all Helvetica.

Universality Image 2

Recently, there has even been a variation of Helvetica, Thai Helvetica, in which Thai glyphs are based on Helvetica letterforms.

Universality Image 3

Roadsigns in Hong Kong use Helvetica Neue as a clear English translation.