Surface-to-air missiles were long a priority of the Soviets. They caused our fliers no end of trouble in Vietnam: this guy got shot down by a SAM
https://en.wikipedia.org/wiki/John_McCain#Prisoner_of_war
The Russian military is organized around a land defense of their homeland since they don't have the natural barriers the U.S. has (e.g. they last got invaded in 1941, we last got invaded in 1812.)
You might think they'd invest in fixed SAM systems but mobile SAM systems are so more survivable in a war because the radar for a SAM is highly visible. You really want to hide those systems in terrain and ambush planes going by.
Systems like that are most effective when they operate in a networked mode together with AWACS airplanes like
https://en.wikipedia.org/wiki/Beriev_A-50
which use a "look down" pulse doppler radar which can see cruise missiles, UAVs and other low-flying threats. This is a great complement to the radar on a Patriot missile battery which is optimized to ballistic missile threats. Russia's latest S-500 system
https://en.wikipedia.org/wiki/S-500_missile_system
has crazy long range, it competes with
https://en.wikipedia.org/wiki/Terminal_High_Altitude_Area_De...
as an anti missile missile system but also it can (try to) take out a distant AWACS airplane with a direct shot.
The Russians DO NOT want an enemy to have air superiority over them anywhere.