Creole again

Both Dutch and the Scandinavian languages have two genders: common
(merged from m. and f.) and neuter.

Dutch went about it this way with the definite article:
First it was

xxx m. f. ne.
nom de de het
obl den de het

Modern Low German still has this system.
Then 'den' was replaced by 'de' and consequently this system
partially collapsed:

xxx m/f ne.
all de het

Danish had, with the suffixed definite article

xxx m. f. n.
all -n´ -n -t

in eg Fynsk this becomes
xxx m. f. n.
all -i -n -t

but in Standard Danish n´ > n, so the result was

xxx m/f n.
all -n -t

Now why do these two (several) Northwestern IE languages reach the
same unique state in non-Anatolian IE, even if they have to take
separate paths to get there? Was this the state of affair in the
Nordwestblock (or Jutish?) language (in which case I'd have to
propose a sociologically layered Northern and Nortwestern Germanic,
with the lower classes speaking a substandard caseless, two-gender
creole)? If not, how come the Slavic languages never 'creolised' (in
that sense of the word), as Piotr once asked?

Torsten