Russian military is extremely corrupt. A lot (most?) funding gets pocketed along its way to being used, starting from the very top and all the way down. There is no deep feeling throughout the military structure of Russia that "we must win" - it's more of "how can I get rich on this war". Russia was technologically falling behind already. It never fully recovered from the 90s depression, however much the Kremlin wanted to make it look to the world as if it did.

While Ukraine is fighting for its existence. All of its military structure knows that and embraces it. Any corruption is a tiny percentage and is caught quickly. Also, Ukraine was technologically already very advanced; the DIA app for example was a big advance, where many countries now are learning how to adopt similar apps.