The straight white men who (largely) built and run Twitter failed to manage harassment on the service. Presumably they just don't think it's a big problem because they don't see it. They have actually admitted this a few times. http://www.theverge.com/2015/2/4/7982099/twitter-ceo-sent-me...

https://twitter.com/bhcarpenter/status/695824384594808832 & https://twitter.com/bhcarpenter/status/695834826432065536