The sources said the summit would not be a serious attempt to discuss issues like privacy or security, but rather "would amount to a right-wing grievance session." Supporting this assertion is the fact that right-wing commentators who have complained of anti-conservative bias and censorship on social media have been invited, as reported in the Washington Post, while Facebook and Twitter, two of the biggest players in social media, have not.
Both companies have had clashes with Trump and his administration. In April, Trump met with Twitter CEO Jack Dorsey and reportedly complained about the site removing a number of his followers. There have also been issues over the shadow banning and actual banning of far-right organizations and individuals on the site. And despite Facebook providing support for Trump during his campaign, it pulled campaign ads which it deemed too sensationalist and banned far-right users like Alex Jones.
Facebook and Twitter were also among a group of 50 global brands who denounced Trump's anti-trans position at the start of the year. There is an ongoing perception among Republicans that Silicon Valley companies have an anti-conservative bias, but it's not clear how hosting a summit without inviting the key players will help address this issue.