This is on top of the documented effort by YouTube to perfect their recommendation algorithm using the best ML minds they got [1] only to polarizing response from its users.
Clearly tiktok has other advantages (homogeneity in some content characteristics, viz. Extremely short videos which probably correlates to their simplicity) and has clearly tuned a fundamentally better recommendation algorithm that even the minds at Google brain couldn't figure out.
[1] https://www.theverge.com/2017/8/30/16222850/youtube-google-b...