This article written by LJ Ellis from Spurstalk may answer your question. Pop being stingy on Lonnie's minutes is not about denying his talent but sending a message to him and the team.

This is my interpretation of the article. Lonnie has a great tool to be an elite defender and he showed flashes of that when playing against the Clippers. The problem was he dropped his man too easily during transition defense, forcing his teammates to pick up his task too often. Imagine the guy that is most gifted in a team defensively does not show the eagerness to guard the opponent best player. It's a dangerous precedent that will have bad influence to the team.

This is why Pop criticized Lonnie's effort publicly (especially for a rookie). I think it makes sense for Pop being so harsh to Lonnie. After-all we all want Lonnie to become a more aggressive and higher basketball IQ player. But if he simply cannot bounce back, then I rather playing him less and just take this as a failed project.