As others have said, Craigslist has an enormous audience which is a self-reinforcing factor.
It also has a practically-unimpeachable reputation as a company which doesn't seem to have much interest in making as much money as it can - only as much as it needs to make.
It does have a number of weaknesses, though. Certain areas are gigantic, useless spam traps. Some territories (the UK springs to mind) are full of basically nothing. Some other territories (like Ireland) are almost entirely uncovered. And a spam-controlled free version of those parts CL is charging for would have a chance at competitiveness.
Nobody's "become a serious threat" to CL because nobody as yet is trying to hit those soft areas while also providing the other services you can get at CL.
Making "a dent in the CL market share" is probably the wrong metric to pay attention to, though - a number of CL-alikes have significant traffic outside the US where CL basically sucks at the moment and has no market share to lose. A quick comparison of Gumtree.com in London versus its CL equivalent shows that it's not Craigslist in pole position.
Again, on localisation of content: CL contains an awful lot of material of no direct relevance to the city you're supposed to be looking at, and all its discussion areas are US-only but propagated worldwide anyway.
I get the strong feeling that on top of all this, CL reinforces its innocuous-little-guy image with its almost wilfully unstyled UI. I doubt that a slick WebTwenny design would help any competitor.
It also has a practically-unimpeachable reputation as a company which doesn't seem to have much interest in making as much money as it can - only as much as it needs to make.
It does have a number of weaknesses, though. Certain areas are gigantic, useless spam traps. Some territories (the UK springs to mind) are full of basically nothing. Some other territories (like Ireland) are almost entirely uncovered. And a spam-controlled free version of those parts CL is charging for would have a chance at competitiveness.
Nobody's "become a serious threat" to CL because nobody as yet is trying to hit those soft areas while also providing the other services you can get at CL.
Making "a dent in the CL market share" is probably the wrong metric to pay attention to, though - a number of CL-alikes have significant traffic outside the US where CL basically sucks at the moment and has no market share to lose. A quick comparison of Gumtree.com in London versus its CL equivalent shows that it's not Craigslist in pole position.
Again, on localisation of content: CL contains an awful lot of material of no direct relevance to the city you're supposed to be looking at, and all its discussion areas are US-only but propagated worldwide anyway.
I get the strong feeling that on top of all this, CL reinforces its innocuous-little-guy image with its almost wilfully unstyled UI. I doubt that a slick WebTwenny design would help any competitor.