Perhaps this is the result of different business strategies. Siglent used to work for the other brands as well so it can enjoy a better access to help, consultations and advices from them, while Rigol insists on its own brand (probably for better access to government funding) so no one can educate them on the art of decision making
And they still do providing mid and low range products to market partners to fill their product range holes.
Siglent have many rebrands including AKIP in your part of the world when last I looked only offered a small range of Siglent products.
Some advances have come from these partnerships, mainly from work with LeCroy however the move recent advances are from within and Siglents worldwide beta team.
And don't kid yourself how Rigol got started, they worked closely with Agilent for a while producing rebrands for them.....