The mains disadvantage of connecting linear regulators in series, is the drop-out voltages add together. Each LM317 needs a total of 3V headroom, plus 1.25V is required for the current sense resistor, giving a total of 7.25V voltage drop!
This is why the input voltage is 32V, for a maximum output voltage of 25V. The maximum input voltage is 40V, since that's the rating of the LM317. It's difficult to get 32V to 40V from a transformer, rectifier and smoothing capacitor. You might be able to get away with a 24V transformer, but it's marginal.
Another issue is when the input-output voltage differential is >15V, the LM317's safe operating area protection kicks in, further limiting the current to 500mA.