Why would a parole officer oppose residential drug rehab for person vs advocating for prison time?

Why a parole officer makes any particular recommendation is sometimes a mystery. Much depends on the past history - both what the criminal record is as well as prior attempts at rehabilitation, history of repeated probation and/or parole violations without showing signs of reforming, attitude towards supervised release, etc.

It's just too vague a question to answer without knowing all the details of the case and the person's criminal history.

I agree with my colleague's assessments. Given the few facts you list, there is no basis on which an answer to your question can be accurately made. In general, probation officers operate under guidelines that indicate a certain type of recommendation to the court based upon the entire record of the person on probation, to include all infractions and the time period in which the infractions occurred. Best recommendation I can make based on the scant facts, is that you consult with a local lawyer who practices criminal defense , and get advice under the attorney-client privilege. There are times when given similar circumstances here in NJ, I have been able to either change the recommendation of the probation officer; or, convince the court to do what my client asked for, even if it meant over-riding the recommendation of the probation officer. Good luck.

DISCLAIMER
This response does not constitute legal advice. Given the nature of this website, it does not create an attorney-client relationship. This answer is provided solely for informational purposes, for you to use as a starting point when speaking directly with a lawyer in your State. I urge you to immediately contact an experienced criminal defense lawyer admitted to practice law in your State before you make any decisions about this case.