Everyone seems to have ignored the part of the article where they mentioned the T-Wolves would want a young player with star potential which the Celtics do not have. As much as C's fans are optimistic about Sullinger or Olynyk, the reality is the rest of the league does not view them as highly. That's the weakest part of the Celtics' offer, along with the fact that the 6th pick in this draft is not as exciting as a top 3 one.
Sullinger is just not somebody you can sell your fans on when dealing a top player. If the Celtics had a top 3 pick then that player could have been the "star-potential" guy but it didn't happen. So now what Minnesota sees from the Celtics' offer is a bunch of B+ guys and some likely late first rounders.
The good thing for Boston fans is that the Celtics might still have the best offer out of the teams Love is willing to go to. We know that even though it's technically a trade, stars of Love's caliber in the NBA rarely go somewhere they don't want which makes it similar to free agency. Only in this case, the pool of suitors is smaller than a free agent situation because you still need something Minnesota finds acceptable to get a deal done.
The question is whether another team will offer what Boston can't, and that's a young player on the level of an Al Jefferson 7 years ago.