多 stacks two 夕 'evenings': night after night accumulating into abundance. Time was the first plenty humans could count — days pile up, and so does everything else. Doubling as multiplication is the script at its most literal.
多 asks and exclaims: 多少钱？how much? 多好啊！how wonderful! 多多关照 'much care please' bows through first meetings. 人多力量大 'many people, great strength' built dams and campaigns; 多喝热水 'drink more hot water' is the answer Chinese boyfriends give to every ailment — a national joke.
Evening 夕 after evening 夕 piling up — MANY.
多 opens China's politest threat: 多谢 'many thanks' and 多心 'many hearts' (overthinking) share a character but not a mood.