Board Thread:Lore Discussion/@comment-103.193.59.119-20170508025131/@comment-203.40.10.214-20170512140339

It could very well have to do with the prophecy, since The Last Dragonborn could very well be the last Dragonborn that is needed.

Alduin's attempt to consume the world earlier than he's supposed to(or rather simply gain power and wage war against humanity like he seemed to be doing) was thwarted by the DB, and now he supposedly will not return until he is supposed to, which is to inevitably destroy the world one day in order to let it start anew.

Meaning that there is no real reason for there to be a Dragonborn after the Last Dragonborn, as the prophecy has been fulfilled and it is unlikely that another will be needed.