Why are flies called flies?

they dont crawl and they dont bite often…..

fly (n.) Look up fly at Dictionary.com
O.E. fleoge, from P.Gmc. *fleugjon (cf. O.S. fleiga, O.N. fluga, M.Du. vlieghe, Ger. Fliege “fly); lit. “the flying (insect)” (cf. O.E. fleogende “flying”), from same source as fly(v.1). Originally “any winged insect” (hence butterfly, etc.); long used by farmers and gardeners for any insect parasite. The O.E. plural in -n (cf. oxen) gradually normalized 13c.-15c. to -s. Slang adj. meaning “clever, alert, wide awake” first recorded 18c., perhaps from the notion of the insect being hard to catch (other theories, however, trace it to fledge or flash); 1990s use may be a revival or a reinvention. Fly on the wall “unseen observer” first recorded 1949. An O.E. word for “curtain” was fleonet “fly-net.” Fly-swatter first attested 1917. Fly-fishing is from 1650s.

Source

They were more noticeable and common than other flying insects, so they snagged the name first.

Probably the first fly was seen at someone’s fly…

Because of all the insects they’re the most fly.

Because they don’t swim?

That’s mostly what they do, and they’re big enough to be noticed (except for the pesky swarms of black flies, or “no see ‘ums” this time of year).