Out of curiosity, why is this?
Actually not all arms need a decoupled counter weight. However most pickup arms are highly problematic.
The type of tube arm in the turntable in question with detachable arm really sing in the 200 to 300 Hz range. Decoupling the counter weight helps lower the Q of this resonance.
Basically moving magnet high compliance cartridges need low mass, low inertia tone arms.
The highly touted very expensive moving coilh medium compliance cartridges need higher mass tone arms.
Turntables are much more complex than they seem. The arm cartridge combination is critical. Almost always there is serious mismatch compromising performance. Ideally the arm and cartridge should be designed as a unit like the old Decca ffss arms and cartridges.
The SME series III arms were designed with the Shure V 15 series cartridges in mind.
I think the best moving magnet cartridges outperform the expensive moving coils.
In my view the Shure V15 xmr was the finest cartridge ever produced. To really optimize this cartridge it needs to be mounted in an SME series III arm with the correct damper in the silicone fluid bath.
I think a Shure V 15 V 15 xmr correctly set up on a SME series III arm and a good turntable gives the best results it is possible to get from LPs. It is way ahead of the pack.
Visitors are astonished at the LP quality here. It occurs because of the selection of the correct equipment.
If you want to get the best from modern moving coil cartridges then you need an SME V series arm. These do not have or need a decoupled counter weight, and in fact should not have one.
Turntables and cartridges are a definite area where paying a lot more for the right equipment pays dividends.
To find a good used Thorens TD 125 and an SME series III and a Shure V 15 xme will cost you a pretty penny, but in my view that is as good as it gets. The first two items are not hard to find, but the Shure is. However the Ortofon Black moving magneth is very close to the spec of the Shure and is a very good alternative.