I think that these companies make a solid effort to curb these types of activities. The problem is that for every account they shut down three more could popup. Although they could be more aggressive with their bans, it would be impossible to extinguish the voice of terrorist groups that use their platforms completely.
The Orlando shooter is to blame for the Orlando shooting. Blaming Facebook, Twitter and Google for providing a platform that ISIS exploits would be like blaming the McDonald's for delivery the food that makes me fat. If it can be shown that Facebook, Twitter or Google actively recruited ISIS to use their platforms then maybe there is a discussion to be had. Absent that, the suit should be thrown out.
It's understandable that in the wake of such a terrible loss of life, that people will be angry and want to blame someone. However, Google and other big tech companies are not able to moderate all the activity that goes through their sites and social media. Finding someone to hold accountable might help heal wounds in the short term, but going after tech giants isn't going to stop the problem of terrorism.
Unfortunately, people use the Internet to spread hate. That does not make the Internet responsible if someone goes out and does something terrible. If Facebook and Google were responsible for what happened, these same companies would have to become the thought police. They would have to monitor what everyone said on the Internet.