The answer isn't necessarily that your products have suddenly stopped working. Skin naturally changes over time, and your routine may need to change with it. Aging, accumulated sun exposure, lifestyle, hormones, hydration, and genetics can all influence how your skin looks and feels.
The good news is that caring for mature skin doesn't necessarily mean buying dozens of expensive products. A thoughtful routine, consistent sun protection, healthy lifestyle habits, and an understanding of what your skin actually needs can make a much more sensible approach.
And for people interested in an inside-out approach, there are also nutritional and supplement options worth researching.