People use youtube for more than 40 minutes at a time on average, FB; 20 minutes. These are because their recommendation systems are, counter to your opinion, really good. Facebook's whole business depends on presenting posts based on how likely you are to engage with them. Other companies might not want to copy TikTok right now because it brings in a whopping $3 million per month, so probably not worth it. There are more reasons behind not copying a business than the ease of doing so.
