merriam-webster.com/dictionary/brevity
It’s pointless jargon.
It’s a lot fewer keystrokes for MS (Morgan Stanley), GS (Goldman Sachs) and MSFT (Microsoft) than it is for AAPL, but it’s a force of habit for some. Once you’re used to referring to firms by their ticker symbols, you do it all the time.
E.g. an ex trader friend still says “spot” instead of “point” when referring to decimal points, even if talking in other contexts like software versions.
I guess if we allowed the first two letter ticker symbol for the missing singles, we could send messages by mentioning a bunch of company names.
Eg "Buy: Dominion Energy, Agilent. Hold: Nano Labs. Sell: Genpact." would refer to our esteemed moderator, and "Hyatt Hotels is pleased to announce special corporate rates for Nano Labs bookings" to this site itself.
[maybe it would be better to use the companies where the corporate name and ticker letter don't match? Like US Steel for X and AT&T for T?]
On a phone, at least in iOS, you have to double tap the shift key.