-help-debug is used to hide "debugging options", and many of them are of no use to the average user or node operator.
In contraast, fee settings are relevant to possibly emergent fee selection behavior such as the lowering of minimum fees. Exposing these settings in the help output increases their visibility and thus the possibility that node operators will voluntarily reduce their fee requirements. Seems that would be a fine thing, akin to volunteering computation and bandwidth.
Prompted by 874e8180858450e7cc597e8ed9b047c35e000dda