On Instagram, posting clickable links on comments are not enabled, The move was taken to crack down on people excessively using self-promotional links in the comments to the extent of spammng.. Instagram’s taking a proactive approach to cutting out spam, and has measures in place to stop people from sharing the same comment on multiple photos as well.
There were report of spam doing the round on Instagram with many profiles getting hacked and misused.
Instagram’s terms of service state that “You must not use web URLs in your name without prior written consent from Instagram, inc.” Infact the community guidelines explain in detail about the same:
"Instagram is a place where people can share beautiful photos of their lives, and when you engage in self-promotional behavior of any kind on Instagram it makes users who have shared that moment with you feel sad inside. This guideline includes repetitive comments, as well as service manipulation in order to self-promote, and extends to commercial spam comments, such as discount codes or URLs to websites. We ask that you keep your interactions on Instagram meaningful and genuine, and note that we are working on reducing comment spam."