You probably see it for the same reason that I still got Connoisseur Class printed on a boarding pass a decade after it had been recast as United Business: outdated labels that still exist in some or other computer system, but do not impact operations.
In large IT systems, almost nothing is identified by its name. This is certainly true of the legacy airline systems developed in an era when it was impossibly luxurious to expend 17 characters to refer to Piedmont Airlines when 2-character identifier like PI was sufficient. Internal codes would be known to the airline's employees, and standardized ones like IATA airline or airport codes would be known to workers in the industry, and full names were only really required for customer-facing materials.
Every aspect of airline operations is plastered with codes. You know that Virgin Australia issued a ticket not because the receipt says Virgin Australia — it might still say Virgin Blue or V-Australia — but because the ticket number begins with 795. You know that a Boeing 757-231 was originally sold to Trans World Airlines, even though it was delivered to American Airlines after its acquisition of TWA, because it ends in 31. You know SkyWest is operating a flight, even though the plane has United's name and logo painted on the outside, because it is coded as OO2884 (in fairness, the passenger probably knows it as UA5601).
If the computer sees SN, it will follow rules related to SN. It doesn't matter that SN went through three owners and as many names in five years. Only the retail customer has an opinion as to whether brussels airlines and SN Brussels Airlines and SABENA should appear on a printout.
Likewise, the airline now known as Swiss International Airlines may be known internally to Aeroplan as LX or CRX or 12345678 or CrossyFlaggyEuros, or some combination thereof. There is some lookup table somewhere that has the old name tied to this code because of a bug, or an outdated record, or some other dependency. But it hasn't been enough of a problem that they've mounted whatever resources are necessary to correct it.