This is exactly what surprised me, that Roscosmos cannot provide launch of domestic satellites. Either there are no rockets for commercial customers, or it will be cheaper in China. And the legal issue of exporting Russian satellites abroad is not yet entirely clear.
My speculation was that the satellites are likely part of a constellation of China, they are made by Sputnix for Chinese customers, so they are not really Russian domestic. My thought is based on the fact that these satellites are small satellites for broadband, Russia is good in making the platform but not in digital chips in baseband, nor miniturized radio chips and TR modules in things like 5G base stations where China is the world leader. So it is a cooperation that put Russian expertise in good use. Since the final (program) owner is Chinese one, choosing a Chinese launch provider has nothing to do with Roscosmos' launch capability or price.
Regulation of exporting Russian space product to China should have been established long ago. There were multiple occations in the past decade that Sino-Russo space cooperation were highlighted in joint statemens/summit between the presidents.