It possibly matters because (at least in the U.S.) this specific data element has substantially different legal obligations than anything else that might be placed into a customer data structure: https://www.govinfo.gov/content/pkg/CFR-2012-title12-vol1/xm...

"(i) General rule. No national bank, and no director, officer, employee, or agent of a national bank, shall disclose a SAR or any information that would reveal the existence of a SAR. Any national bank, and any director, officer, employee, or agent of any national bank that is subpoenaed or otherwise requested to disclose a SAR, or any information that would reveal the existence of a SAR, shall decline to produce the SAR or such information, ..."

A bank might not want to aggregate data, within one IT system, if part of the data has the very unusual property that a subpoena must be declined.