Why are i.e. (id est) and e.g. (exempli gratia) abbreviated with periods between each word and etc. (et cetera) not abbreviated as et.c.?
The reason is because the original abbreviation of the phrase "et cetera" was "&c.", and in fact the ampersand existed as a common "letter" in English for quite some time. Instead of referring back to the original Latin, when ampersands fell out of use "&c." turned into "etc.".