They’re flying these in very low and slow, which is hard for SAM radars to detect and lock on to unless you’re right up next to them – and once they’re past the front lines Russia doesn’t have many (if any) point defense installations.
In fact I imagine that the economic impacts of these attacks may be a secondary goal, and the main intent is actually to force Russia to pull SAM systems off the front line and redeploy them across the Russian interior to defend facilities they thought were safely out of Ukraine’s reach. The fewer defenses on the front line, the more capable Ukraine’s air force is to support efforts on the ground.