[Sebb767]

It's usual in chats, not for formal writing like officially announcing your resignation. At least that's my impression.

[TheRoque]

Maybe that's why it's used ? Twitter is just addressed to the public, so it's not official in any way, it's just communication. The lowercase casual style is only used to drive empathy probably.

[vikramkr]

This is the sector of the economy that ipos in cargo shorts I don't think formal writing would be expected or appreciated

[dkryptr]

To be fair, that's not a very formal resignation. He just... quit.