Ah, okay - sorry. One of the main problems, as I see it, comes via the use of the standard S-300/S-400 missiles that simply don't have the best burn times & are primarily designed to be lofted above, before ultimately falling on, their targets (aircraft), & as a result, they simply lose too much energy & cannot curve downwards fast enough to intercept something like ATACMS.
In general, it looks like what has happened, here, is that The Soviets starting fielding air defense systems like The S-300V that, at least in theory, would be able to deal with the traditional ballistic missiles of the time like The Pershing & Scud that aren't exactly known for their maneuverability, so in response, we developed ATACMS that can snake all over the place with its long burn time before ultimately falling on, say, a SAM site, thereby making it very difficult for The S-300/S-300V interceptors to be able to take them down, as The Soviet missiles would have long since stopped burning & would have lost too much kinetic energy to be able to move in time, etc.
Ironically, this makes their older missiles, like The S-75 (even though almost no one uses them, anymore) & The S-125 ideally suited for the task, as just like The Buk that has proven to be their most effective system at dealing with ATACMS, those upgraded older missiles have excellent burn times, good-to-great speed, excellent maneuverability, & perhaps most importantly, start by shooting on the way up via an adjustable launcher, as is the case with The Buk, & calculating the point of interception is just basic math, not to mention the fact that even the improved legacy missiles are cheap as hell & are much more accurate than their predecessors.
Sure, hit-to-kill is great & everything, but it's also extremely expensive, & the real key to shooting down ATACMS, etc., is to use a missile that is still under power at the moment of interception, as that gives you a much larger margin of error. Russia might not see it, but we've actually made their job much easier for them, imo, plus it's the ultimate troll move, lol.
For perspective, we could have done the very same with The Hawk, as like The S-125 it has excellent speed, maneuverability, & a great burn time, but nooo...we just decided to give them all away.