It was only last year that majority of those polled supported legalizing marijuana: http://www.people-press.org/2013/04/04/majority-now-supports.... At the time of the last dot-com bust (2001), it was 60-40 against legalization. Since actual voters skew older and more conservative, it's totally unsurprising that it has only been in the last few years that legalization efforts have gained traction.
Yet legalization of marijuana is just the first step, and one that's easy to take for middle class voters, whose kids may use marijuana or who may use it themselves. It'll still be a long, uphill battle to convince these voters that it'll be better to disengage from the drug war completely. A lot of the people involved in drug distribution are not sympathetic figures to the general public: uneducated, often minorities, and usually with long criminal records. The idea that disengaging from the drug war will mean "going soft" on these people will be a powerful one.