Antonelli and Kornfeil penalty?

Why are they receiving a penalty (1.3 and 1.8s respectively)? When Antonelli rejoined the track he waited for the people behind him to catch up with him, and even lost a position. So why did he receive a time penalty anyway?
Submitted May 20, 2018 at 10:28AM by Rickyrider35 https://www.reddit.com/r/motogp/comments/8krmgf/antonelli_and_kornfeil_penalty/?utm_source=ifttt