Judicial Activism Antonin Scalia-style

In Maryland v. Shatzer (http://www.supremecourtus.gov/opinions/09pdf/08-680.pdf), Antonin Scalia and the Supreme Court engage in some good old fashioned "legislating from the bench." The Court had decided that a request for legal counsel (in response to question per the Miranda warnings) only should last 14 days. Here is what Scalia writes:


Confessions obtained after a 2-week break in custody and a waiver of Miranda rights are most unlikely to be compelled, and hence are unreasonably excluded.

The question here is how did the Court arrive at this conclusion. It appears that they pretty much just made it up. I thought the legislative branch was supposed to do fact-finding and engage in these kind of political judgments . . .