It is not just about the tax. The NBA made it more difficult to build your team if you go above the first apron, and made it punitive to go above the second apron. The first apron is only a little above the tax, so teams stuck at the first apron (which is most teams given the rules) will tend to get below the tax.
But in this world where you are now regularly capped at the first apron, having two players who make what the Js do is probably prohibitive. You can do it for a bit, but eventually the roster holes are going to be unpatchable. I think the Celtics have looked at their roster which somehow was very successful last year, noted how much production was giving by guys making under $3 million, and determined that probably is not sustainable. Either those guys need raises, which will bump you back to the second apron, or you have to get lucky year after year hunting for bargain players.
They do not need to make a trade this year. If they do not get an offer that works, they will not. But they probably do before Jaylen?s contract is over, and coming off the year he had, with three years left on his contract, this will probably be peak value.