The suits were filed because Ericsson said it could not reach a license agreement for its patents with Samsung on fair, reasonable and non-discriminatory (FRAND) terms after two years of negotiations. Samsung was asked to pay the same rate as its competitors, but Samsung refused, according to Ericsson.
Samsung had licensed Ericsson patents before. However, according to a statement released by Samsung last week, Ericsson demanded "significantly higher royalty rates for the same patent portfolio," adding that it planned to "take all necessary legal measures to protect against Ericsson's excessive claims."
Samsung used to license these patents, then stopped paying. They knew a lawsuit was coming, and decided it was a fight worth taking. I have no clue whether the fees requested by Ericsson are unreasonable or not - but there's no need for conspiracy theories or ulterior motives on this one.