Another thing to consider, I read the other day that there were intercepted calls from the Russian Railroad honchos which indicated that they were concerned about a serious shutdown of the system due to, and I promise I'm not making this up, ball bearings (cue Fletch). Another thought may well be that by doing this, it will further exhaust an already extremely strained Russian logistics system. Basically, they may well have Intel that Russia has no real meaningful way to respond to this incursion, beyond air power, at least not in any meaningful quick way. Given that Russian pilots are terrified of getting anywhere near the Ukrainians due to hand held anti-air, that may well be moot as well. In an effort to bolster or even rally a defense for Kursk, the Russians may well completely starve other areas of ammo, food, etc.
Someone mentioned Sun Tzu above, and one thing he was big on fighting on the ground you want to fight on (classification of terrain, I believe he called it).