I thought not needing words was because people often watch them on their phone in public without sound. Who are these people that can't enjoy listening to spoken words because of illiteracy or ignorance?

I mean... Tiktok's hallmark trend has always been people doing "TikTok dances", which involve audio, so...

But, besides that, TikTok became the titan it is today during the pandemic. When everyone was indoors (not outside).

Per Google's quick answer, when searching "When did TikTok get really popular?": "TikTok's global popularity surged in 2020 due to pandemic lockdowns, with consistent growth since 2016, surpassing competitors in downloads by 2018."