It might be because most of the social platforms on that list don’t really fit the mould of a town square in my eyes. WhatsApp, YouTube, Snapchat, FB, FB messenger and others I recognise aren’t shaped in ways that look like public debate and are generally more siloed or are creator platforms.
Twitter seems to me more like an open free-for-all where any text can get amplified and publicly interacted with and very little is behind private accounts/groups/silos and anyone can easily contribute.