Is it? I.e. winning small on lottery is not that improbable. It still has negative expected value, and so do fantasy sports. The difference is that winning big in lottery is uniformly unlikely, while winning big in fantasy sports is mostly tied to your Microsoft Excel skills. Which:

a) makes me believe that your assumption that "winning fantasy sports betting is far, far more likely than winning a lottery jackpot" is incorrect, and in fact for an average Joe, the reverse is the case;

b) suggests that the biggest advocates of fantasy sports will be people who believe they're good enough with Excel and statistics.