Though historical accuracy is no longer a major concern, maps are still loosely tied to BRs, battles that took place later in the war can be played by playing on higher BRs.
This is an interesting but imperfect feature that will still require more campaigns to work as intended. (But Veekay has already made everyone all too familiar with that anyway.)
Back in early 2024 when the Battle of the Bulge campaign was released it was only “temporarily” added (alongside Normandy campaign) to BR1-3 so new players could enjoy the new map as well, which became quite permanent by now.
By now everyone had his fair share of chances to play it, so it should become unique to BR3-5 because maps changing with BR gives a far more unique experience and a feel of “progression”.
Instead of the Bulge campaign, BR1-3 Axis and Allied players should see more Tunisia campaigns instead (which is the least likely to get campaign by the MM at the moment).
I believe it’s needless to say that enjoyers of low BR equipment can still enjoy the Bulge experience in all of its glory in custom matches.