The war of attrition is hurting Russia more than Ukraine, because Ukraine has better help, and Russia has way bigger losses due to pushing without sufficient equipment.

can easily afford to slaughter several 10.000

But that's just a weeks worth of casualties at the current rate! And Russia is already stressed to the limit from shortage of workers, and their economy is collapsing. With continuously worse military supplies for Russia, while Ukraine is improving, there seems to only be one possible result. Even Russia can't continue the meat attacks forever.

he may be worried that admitting defeat would weaken his position too much.

I think this may be a major reason, he simply doesn't dare face the consequences of losing the war, and having wasted lives and collapsed the Russian economy for nothing.
So he is setting Russia up for extending the war indefinitely. But I think Russia will collapse soon, everything is going downhill in Russia, and for no good reason.
Ukraine on the other hand has very good reason to fight, they are fighting for independence and freedom from the Russian regime.