It is true that these offsuit hands COULD be raised after limpers since they stand to win more than their fair share, it is often better to forego this slight-to-moderate pre-flop advantage in favor of a large advantage (if the flop hits you).
By playing the hand this way against loose limpers, you can usually make up postflop for the amount you gave up preflop. For more information on raising loose limpers, check out Izmet Fekali's articles:
Rammin' and Jammin' Preflop, and
Implied Odds (Preflop).
I feel that these are some of the best explanations of loose-game strategy available.
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