The reasons as to why they didn't play, not even talking about injuries are very different to Kalulus situation.

Gabbia & Ballo-Toure wasn't up to standard of what was needed from them, something that resulted in Kalulu and Florenzi taking over as they preformed much better.

Castillejo had 2 people that, again, preformed better then him. Bakayoko had 4 people that preformed better then him and subsequently they played instead.

Maldini, Lazetic and Pellegri simply wasn't ready and still isn't.

There is a huge difference between all these guys and people like Kalulu who has consistently showed their worth and that they can be starters VS players that are either

A. Unproved B. Not shown enough quality or C. Not developed.

Adding to that we have 2 RB that are, to different extents injury prone and Kjaer who is old & suffered a big ACL injury which could set back his play.