They are afraid of https://en.wikipedia.org/wiki/Buk_missile_system a very good technology that the Soviet Union developed which punches above its weight in situations like the Ukraine war because the mobile radars are hard to suppress with these methods https://en.wikipedia.org/wiki/Suppression_of_Enemy_Air_Defen... I have seen a huge number of Buks in various conditions in video footage from the war, one of them wa…
Starting in WW2 and moving forward each side took a very different evolutionary path in terms of air power and air defense. The west relied far more on combat air craft for air defense because that's what worked on the western front. The soviets had a very different experience in the war and had to fight while being under constant attack from German airpower through most of the war. So they focused on giving their army its own air defense capability.
Fast forward 80 years and western militaries will have a few SAM systems like the larger patriot and the Stringer MANPADS but will primarily rely on fighters to clear the skies. While the Russians have a SAM for every situation and a much smaller tactical air force. The west has also since Vietnam spent a lot of effort on defeating Soviet style SAM systems with improved SEAD tactics and equipment whereas it was never a concern for the Russians because there isn't much in the way of SAMs to suppress.
For those reasons you end up with the ironic twist of Russian SAMs being especially effective against Russian aircraft because they didn't prepare to counter their own systems. They DO have anti-radiation missiles and strike aircraft but not as many as the west and their doctrine is not nearly as well practiced.