There is one big difference between the Cardinals interest in Giancarlo Stanton and the situation right now with Nolan Arenado.
When the Cardinals made their bid for Stanton, they had been frozen out of some big ticket pursuits, Mozeliak had even brought up the "bridesmaid" tag, and ownership had said that it wanted to win a pursuit, not be happy to participate. All of that was going on in the backdrop, and they needed a middle-order hitter. They also acknowledged the benefit of getting a star through the doors to get fans into the seats. That was the atmosphere, and that was the payroll, and that was the roster situation.
As of today, they are about a year removed from signing Goldschmidt to the largest contract in club history. They traded for their All-Star, their MVP-level player, and they signed him. That is a significant difference when you're talking about what drives them at this point, vs. what we know about their pursuit of Stanton.