Because the Soviet sniper is generally shooting less numerous, more expensive models.
This argument already wasn't significant with introduction of
- USF (4-man team weapon crews, some 4-man squads, somewhat expensive 5-man mainline inf)
- OKW (5-man cheap mainline infantry, possible 6-man long-range doctrinal PFussies)
AND completely died with addition of UKF (4-man team weapon crews, 4-man mainline infantry almost as expensive as Grenadiers).
But that's not even point.
The question is - why Soviet Sniper should have same durability, if it fights against squads with much higher long range DPS?