Ukraine might be on the brink of collapse but it's still capable of inflicting losses to the Russians, especially using drones. As the Russians themselves have said, the nature of warfare has changed a lot due to the introduction of cheap small drones in the battlefield. Any significant mass of men, weapon platforms or ammunition is instantly targeted. Therefore, the tactical approach now for both Russia and Ukraine is to use very small groups of soldiers in any attack, so as not to attract drone attacks. Furthermore, massed artillery is no longer practical due to the target they would present and neither is storing ammo/supplies in large quantities anywhere near the front, as they'd be extremely vulnerable to drones.

Also, we should keep in mind that due to constant satellite surveillance, all the above can be identified and targeted very easily. Also, the surveillance makes it hard for Russians to draw or prepare to execute massive pushes, as they would be easily anticipated. Therefore, they try to keep things moving everywhere all at once, and wait for advantages to develop before pouring resources to those sectors that would prove the most beneficial.

Hence, any advances made are small and incremental. The advantage that Russia has now is that it can perform these advances everywhere at the same time, and, because the Ukrainian ability to respond has been minimized, most of these small advances can be immediately successful.