we dont really need 3rd or 4th round picks so i rather just keep Evans
Yeah. I get the motivation of trying to "make room" for a young guy looking good in camp...but these aren't necessarily the sort of things you need to be in a huge rush to do. Looking good in camp doesn't always mean that guy is fully ready for the long grind of an entire NHL season.
And on the other end, more layers of depth > less depth. Inevitably, injuries will hit. Plus, Evans isn't a spectacular player, but he's at least a solid, reliable vet with some versatility and ability to take on some less cushy offensive minutes, eat PK duties, etc. I think that's a guy you'd want to keep around for a bit to help continue to insulate some younger players if you can.
And finally, i think Evans is probably the sort of player who is worth a little bit more at the deadline anyway. Where teams will actually pay a better draft pick/prospect for defensively reliable 3rd/4th line depth Centers who can kill penalties and aren't an utter black hole offensively. Where they like to stack that sort of depth as deeply as they can. Where they often have injuries and more "effective cap space" to work with in building that up.