Russell defined "truth" to be that which our beliefs find in-the-world.
Pascal defined "God" as that which is (perhaps (Immanent)) in-the-world but not of it (Transcendent).
Thus, the "wager" of Pascal is objected to as "irreal," as based upon something that Russell could not find among the atoms.
A further set of objections to Pascal's wager:
"God is Omniscient," hence is aware of the motives of Pascal's "bettor." Thus, unless the "fear of God" ---> genuine "love of and for God" (which is usually generated by an awareness of Love by God for the individual), the bet is perhaps "formal" but not "genuine." (See the soteriological parable of the "widow's mite.")
And: "what God" and "what rules" are in the wager? Generally, Pascal's God = the God of Abraham, Ezekiel, Christ Jesus, and suchlike. The rules for this God ~ = "Love God completely, and colleague as Self," "Love as Christ (Jesus), Truth, loves," and the "10 Commandments."
Russell was a materialist (atomist) and atheist (it would have been more logical for him to have been an agnostic). Human "feelings" as foreshadowing divine Love were not prominently featured in his "reality," to describe the behavior charitably. In the Christian and other perspectives, such character traits are not particularly glibly modified when in the Presence of the LORD, hence the problematic of salvation re such difficulty of changing one's conformance to kindness, justice, humility, consideration for others, etc. (i.e., sincerely moving from "childish" to Childlike).