I would like to recall the "Demographic Yearbook 2011" of Central Statistical Office (GUS), [stat.gov.pl/cps/rde/xbcr/gus/PUBL_rs_rocznik_demograficzny_2011.pdf]
OP: ...stable, longstanding, traditional societies of southern, central and eastern Poland, This includes ... divorce rate ...
The sections (34-55) of the Yearbook , dealing with divorces across provinces, may be of interest. Make sure that you compare the relative, not the absolute, data. Draw your own conclusion, but here is just one example.
A shortened list of divorces in the >100,000 towns, per 10,000 population
(26.8 Gorzów Wlkp)
(24.0 Zielona Góra)
If the Western and Northern provinces are to be considered the rootless evils, why do we have so many towns from Central and Eastern Poland among the 10 top divorce culprits, including Toruń, Częstochowa and Białystok?
Perhaps, as somebody already pointed it out, this might be caused by internal migration. Take a look at some plots at the end of the GUS presentation. For example, the internal migration plot shows sharp peaks, going both ways (rural=>urban and urban=>rural). The peaks are centered around 30-34 year old men, and 25-29 year old women. Do not be mislead by relatively small values of these peaks: You would need to integrate those plots to get some ideas about total numbers - or better yet: go the section "internal migration" and compare the tables. And do not forget about the external migration either.