Why is particular token missing in LALR lookahead set?
In state 0, R ::= ⋅L can only be generated by S ::= ⋅R. In L ::= ⋅* R, the dot precedes *, not R, so no further items are generated by it.

The dragon book uses this grammar as an example of the inadequacy of SLR, and the correct computation of the lookahead in this case is an instance; the SLR algorithm bases lookahead decisions on the FOLLOW set rather than actual lookahead possibilities in the state, which will eventually lead to a shift/reduce conflict on lookahead symbol =.