Product prices are determined by the willingness for consumers to pay for them. Families (especially kids) have different priorities and search habits to IT professionals, for example, which appears to be a common persona for them. It is likely that they bet that the four extra users and child friendly options are what families care about, rather than a high number of searches. It's also likely that families simply don't need that many searches, and in limiting them to 2,000, they discourage abuse (six professionals purchasing one family plan).