For the same reason you shouldn't be bullish in 2019 (WAY more money to go around), it's a losing game trying to beat Boston's asset collection. Seriously, look at everything they have if a true superstar were to come available. They could get Kawhi in a snap of a finger if he would commit to a deal. Davis unhappy? Boston's got him.
I'm not saying we shouldn't collect assets, but I personally think being a legit playoff squad with max cap space is our most valuable asset this Summer and next.
Salary dumps are great if we are rebuilding or on the fringe. Right now we need real tangible players that can contribute. Being a team of our caliber with space could allow us to not only get a max star player potentially, but also get some serious contributors for cheap (which by the way, are just as valuable as first round picks to many teams)