With Russia outgunning Ukraine’s artillery at an estimated 15-1 it looks like the main tool for halting Russia’s advance is about to start running at marginal effectiveness. Ukraine’s main industrial hubs are either already occupied, have incredibly difficult issues with supply lines, or have sustained physical damage, and artillery has been one of Ukraine’s most effective tools at slowing the Russian advance. The fact that Ukraine is simply using this ammunition faster than the west is willing to donate and faster than Ukraine’s domestic production can keep up with does not bode well for their ability to mount a meaningful defense for much longer. The last aid package passed by the US bought Ukraine only about 2 weeks worth of artillery shells.
They've been either bombed out (because it's hard to keep the locations of these factories secret) or captured (most of these industrial facilities were in the east anyway)
any soviet ones were never secret from moscow in the first place
And Moscow was going nuts with targeted missile strikes for weeks on end during the start of the conflict.