The Suns are limited to re-signing Smith for more than the declined option: $4,670,160. They can’t pay more than that, even if they have the cap room to do so. That, obviously, makes it very easy for a rival team to bid higher. Additionally, the declined option is basically radioactive: Any new team acquiring Smith this year would be affected by the same rule. Thus, the Suns can’t get anything useful for Smith in a trade because the acquiring team would likely lose him after the season. (Unless he played badly, in which case, who cares.)