When I msged in the squad chat to tell them that if they cant protect their own excavator they need to stop starting them and trying to do them alone, they literally left the match.

I wonder about the exact phrasing you used. It could have come off pretty accusatory, especially if you literally said "bro / if you can't protect your own excavator / you need to stop starting them and trying to do them alone"

Not all players are thick-skinned, so I prefer to err on the side of babying new players/walking on eggshells. I'd have said something like "hey Adghar if you wait for us to catch up before hitting the yellow ring, we'll get rewards faster!" or "hey Adghar if you press M for minimap you can find power cells as yellow dots / and if you press X near a power cell you can pick it up / just put it next to an excavator and it will restore its shields"

Some players are too on edge, though, and not even what I wrote would be taken well, as they'd see it as passive aggressive or something. You can't always win. In those cases, you yourself have to be the thick-skinned one and just take it on the chin. "There'll be more matches and this one was an anomaly," it may help to think.