I can answer your first question.
Early spelling reformers (See page 5 & 6 here) wanted to
"alter spellings in such a way as to reflect the Latin or Greek origins of the words. In their hands, the spelling of DETTE was changed to DEBT, DOUTE to DOUBT, and SUTIL to SUBTLE in order to reflect the origins of those words in the Latin words debitum, dubite and subtilis, respectively [p.6]."
- For Teachers