The problem with NiMh batteries is that the state of charge "full" cannot be determined on the basis of the single-cell open circuit voltage or with a specific end-of-charge voltage as with a LiIo battery. That should be the main reason why there are no NiMh battery packs with balancer connection.
If the NiMh batteries were equipped with balancer connections, the control of the chargers would have to be adapted extensively.
A separate individual cell evaluation of the delta peak of each individual cell would be theoretically conceivable. As soon as a cell was recognized as full, almost the full charging current would have to be discharged at this cell.
Another approach would be to generally only charge such batteries with single chargers connected in series only via the balancer connections.
In both cases, a considerable additional effort for the charging equipment.
A further development of the chargers in this direction is no longer to be expected from the charger manufacturers because of the generally diminishing importance of NiMh battery packs.