some keys are more equal than others ...

More quote:

"Unequal temperament was practiced in olden times when music did not
wander far from a few keys which were favored in the tuning. You will
see (...) how a temperament could be set in such a way as to favor a
certain key (...) and also those keys which are nearly related to it;
but, that in favoring these keys, our scale must be constructed
greatly to the detriment of the 'remote' keys..."

somewhat clearer what "try to favor the flat keys" might mean?
~~~T~~~