The reason is simple in that gutters only come in a limited number of colors while paint colors are infinite.
Replace gutters before painting.
To answer your questions more specifically.
If they are due for replacement getting them done before or during the exterior painting process makes sense especially if your painter has the chance to paint the gutter boards once the old gutters are removed and before the new ones are installed.
If you are replacing them chances are you are limited to a choice of colours.
If you can prevent your gutters from clogging then you can stop a lot of those gutter problems in the first place and you won t need to worry about gutter painting or gutter replacement.
It s important to clean your gutters seasonally to prevent debris buildup.
It s constant runoff from your roof that would eventually cause problems.
If there is paint peeling on the sides of your house it may be an early sign of water damage.
If your rain guttering systems are working correctly the side of the building should be protected from excessive moisture.
Before exterior painting or replacing gutters.
If you get some rain or even a storm before the new gutters go up that s no big deal.
Often problems with gutters sagging and getting full of debris begin with gutter clogging.
Pull the gutters down and paint when the forecast looks nice.
If you want a new look for your gutters should you paint them or undertake a gutter replacement.
Avoiding the need to paint.