Thanks. Here's an excerpt from one of the articles you linked.
Brad Penner-USA TODAY Sports
March 6, 2019
Red Sox starting pitchers cleared for spring debuts
By Matt McCarthy, 985TheSportsHub.com
Chris Sale, David Price, Nathan Eovaldi, and Rick Porcello are all set to make their spring training debuts in the coming week as the Red Sox cautiously work to get their top four starting pitchers ready for the regular season.
The Red Sox have avoided using their starters in Grapefruit League action up until this point in an attempt to manage their workload. The decision came after the team used Price, Eovaldi, and Porcello heavily in both the rotation and the bullpen last October. Sale, meanwhile, is coming off a shoulder problem that limited him at the end of last season.
The word 'caution' in various forms appeared in several of the articles.
My main takeaway from the articles is that the team was very concerned about the impact of the postseason run and the fact that the starters also pitched those high-stress innings out of the pen.
I don't see it as some brilliant new-fangled scheme to have these guys peak later in the season. I see it primarily as an attempt to preserve their health.