Serif fonts were used in print media for ages but when computers came around sans serif became significantly more popular as no longer was there the legibility concern with dodgy pigment applicators etc.
People started to switch to sans serif fonts more and more and would seek out an alternative to the widely defaulted Times New Roman in early days. They'd open the alphebetically sorted fonts list and what did they see at the top?
Arial.
Keep in mind, when personal computing started out, we didn't have a ton of fonts packaged with the system to start with. Just a handful. Arial has pretty much always been there.