It may be totally irrelevant or off topic from what others asks... but it's been quite a long time that I'm keep thinking of this question whenever I have to choose a font for my UI design!
I've done my homework and searched for this and similar questions but nothing came up!
I'm pretty certain that there must be a good reason that Arial still in use amongst top businesses like Google Search (despite they have material design dedicated website), Gmail, Amazon, eBay, StackExchange and many many more...
Apart from being free and familiar to people, what's its main purpose that this font is still in use?
Can't big businesses like Amazon, eBay and many more can't afford a good premium font that would not only look good but also be part of their branding? Of course they can but the question is why they don't!!!
Is one business/company looking at another for choosing their font or what?
NOTE: Everyone know that Arial is easy to read etc. so obviously this matters UX-wise, so please answer something that's not abvious...