Because it is possible FSG is capping this team at 225M / is unilaterally saying no to any huge FA signings for pitchers over 30... so that is the only other feasible way.
I'd prefer it if they just signed one of Snell, Fried or Burns but yeah, recent history pretty much shows that they won't. So who do you trade?
Duran- probably hit his peak. Probably would fetch the most return. Centerfield defense would improve (not saying he's bad out there) by putting in Rafaela there full time. Offense big drop off (even though I think Rafaela will improve to around a consistent .750 OPS guy). Rafaela would "balance" the lineup more if Duran was dealt.
Abreu- GG caliber RHH. Can't hit lefties. Or maybe can but hasn't really had a chance to yet. Likely would need to be paired with another good prospect, though second tier type, to bring something of equal value as Duran. Could be replaced by Anthony who looks to be a more complete hitter. But we know Abreu is good. Anthony still never played a ML game.
Rafaela- would be harder to get a good SP for him. Likely would need to add a higher tier prospect to get someone and that someone would likely still be on a lesser rung of SP's than the guys who Duran or Abreu could bring back.
Grissom- value is very low but I could see him paired with Abreu. Campbell could take his spot?
Casas- juggling around for his replacement wouldn't be too hard. He could probably bring a better return than anyone not named Duran, but he's a possible, with high liklihood of hitting that, middle of the order 35HR threat with great OBP.
ML "sweeteners"- Valdez, Hamilton
Mayer- value is high but not as high as Teel, Duran, Casas, etc... would pretty much put him as a similar value as Casas. Injuries may be chronic. Blocked by Story, although we know the story on Story. There's some SS depth behind Mayer. Rafaela could be that if needed. Campbell there?
I don't really have to strain hard to see how all of these guys with their injury history can all exist on the same roster, but it would definitely be one without O'Neill and Yoshida both