I have NEVER had a S. purpurea flower..in 16 years of growing them!
no idea why..
And I have other Sarrs that dont flower at all until I have owned them at least 3 or 4 years..
I think even if they are "adult" plants, it takes several years for them to get established in a new home before they will flower..
It just takes time..
and yes, just keep your plants outside all the time..
there is no reason to carry them in and out..
if its above zero degree Celsius, just leave Sarracenia outdoors.
dont even worry about bringing them indoors unless its below zero degrees C.
Looks like most of Poland is zone 6..a bit cold for overwintering outdoors.
you will probably have to find a cool indoor place for winter dormancy this winter..