‘View previous replies’ on Instagram and LinkedIn… but why?

Instagram and LinkedIn both show the most recent replies to comments first, and then you have to click to 'view previous replies', effectively working your way backwards towards the first reply. So if you want to follow a thread of conversation you have to click many times (depending on how many total replies there are) until all the replies are visible and then read back through them in the order they were posted. I just can't figure out why this is the way they both choose to do it, as for me it provides a frustrating experience on the regs! Can anyone explain the logic behind this pattern?