As brake fluid ages, takes on moisture, is heat-stressed, it's pH drops ...meaning the brake tube's internal environment moves further away from the metals' (and rubber) "Safe" range is, the more corrosion can/will occur. To what extent this affects the ABS valves, I can't say. It would probably have to sit a long time to seize. But maybe actuating them through a bleed process made a difference. Or the vibration of the process made a weak electrical connection 'good' again.
Most of what I've seen online are weak or cracked solder joints on modules ...by looking at online 'fixes'.
Regardless, it's important to replace the fluid every so often to maintain an internal higher pH range where the metals/rubber components are 'happy' and help avoid corrosion.
Edit: (Pretty much the same is true for coolant)