why the "Popular"/"Top"/Trending" column is always on the top part? or it's on the first page? why it's not the "Recent" or other categories first? What is the reason behind this?
Since the algorithm already knows which topics are relevant and interesting its only logical to display those on top/a prominent spot so you can keep the user/reader on your site and basically redirect him multiple times within your site.
Other categories don't really have the power to do this, maybe a "similar to this" categorie could achieve the same for single users, but the categorie usually is placed really close after a given topic.
If I understand your question correctly, your're asking why websites put more weight towards what's popular rather than what's new?
It's about drawing the user in and keeping them on your site to either sell something, or make them spend more time on the site and see more advertisements (so more profit for the business). This is also why sites encourage you to add favorites of something (to mark you like it) so with new visits they can immediately target you with things that are most likely to keep you coming. This practise increases user experience, but it's heavily accompanied by generating more income. For the user this has the benefit of you not having to trundle through things you don't care about and being able to see the best stuff (for you at least) straight away, increasing enjoyment and the time you spend browsing.