I think it's partly that and also partly depending on how comfortable the two GMs are with their jobs
If you trade to a rival and give pieces that end up being significant, you do run the risk of being "that guy" that dealt a guy that comes back to haunt your franchise and all that.
But yeah, teams do trade more these days. But there is a big difference between trading a guy you see 2 times a year as opposed to 5 or more depending on playoffs.