Apparently one of the very reasons for this difference is the TikTok's praised recommendation algorithm that tends to deliver "more to watch" features that people actually want to watch after one reel has finished.
According to Comscore data Americans spent 5 billion more minutes with TikTok from June to July. While TikTok has half the audience of Instagram its users spend DOUBLE the amount of time on the platform.-- Flora ESPN Research (@ESPNFlora) August 25, 2020
To counter the threat, Facebook is rolling out direct TikTok copycat service dubbed as Instagram Reels, set to roll out globally soon.
Facebook has used similar tactics against its other rivals, too. Instagram's one of most popular features, its Instagram Stories, is a blatant ripoff of SnapChat's similar feature.
Facebook actually tried to buy TikTok back in 2016, but failed.
TikTok has now almost 700 million unique monthly users. Company is in middle of U.S. - China relations fight, as TikTok's Chinese ownership is questioned in United States - and there have been plans from American companies to buy the service.