To be fair, SP3 was released in mid 2008, 7 wasn't released until late 2009, and XP had a greater usage share than 7 (and Vista combined) until early 2011.
It is a sensible decision to only target Windows 7+, and the only reason to stick with XP would be specific compatibility with older programs, but it is a stretch to dismiss XP as a product that came out a decade ago when it still has an enormous market share.