While the Rangers did try to work out an extension with Strome last season, it looks like the gap is just too great, and so he'll leave after three seasons that often saw his name come up in rumors.
As for Copp, he could be looking for as much as 56M a year, which would probably be too rich for the Rangers given what he brings to the club, and that money could probably be spent on a more dynamic player.
Vatrano's departure is likewise, not unsurprising. While he was a good contributor to the line-up, the Rangers oversupply of wingers as well as his relative cost (probably in the $3M-$4M range for multiple years) wouldn't have made sense.
Both Arthur Staple The Athletic and Vince Mercogliano Lohud explored options the Rangers might consider.