Several reasons.
replyFirst, a long-running SEAD / DEAD campaign by Ukraine last year and early this which thinned Russian air defence throughout occupied territories and left Russia with difficult deployment decisions for what remained.
Second, improvements to drones (speed and EW resistance) and expanded production - meaning the air defence can be saturated.
Third, Russia's vast geography itself, leaving countless approaches to targets impossible to defend.
"What air defense doing?" is apparently still an unsolved riddle.
replyMasses of drones. Some get shot down, but not all.
replyBold of you to assume they have many defenses left.
replyTheir lines of 50+ years old junk which have been rotting for decades because of corruption and are operated by low iq conscripts with no training?
replyA mystery really...
Saturation
replyRussian air defence equipment bad, organised even worse, and has been severely degraded over 4 years now.
replyIt also seems like a bit of a game of whack-a-mole. UA put logistics/distribution centers under threat (wildberries) and refineries under threat, so the Russians moved their scarce air defense resources around on the map in an attempt to cover those, but oops, that left little or nothing covering the yandex datacenters and similar. There's not enough to go around to cover all of the possible geographically distributed pain points in the economy.
replyThe are largely concentrated around Moscow to defend the "brain" of the country, as well as personally Putin himself.
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