Severe use of small disc , small caliper and small fluid reservoir generally results in the fluid being boiled for want of a better description.
Not much you can do about it. I'd definitely change the fluid if I'd had the brakes reach that stage.
Used to tear round on an XR650R SM with the standard front brake which usually ended with an excursion into the boonies, changed to a 320mm rotor, larger caliper and suitable master cylinder and was able to stop when I wanted to.