Because a significant number of people like the idea of being super-rich instead of kind of rich, and when the jackpot gets higher more people play. There are already other lottery games with lower payouts, the fundamental point of Powerball is a big jackpot. It’s like asking why soccer doesn’t let players grab the ball and run with it, it wouldn’t be the same game if you made a fundamental change like that.
I think it would be more interesting to split respondents between ‘people who just have a job’ vs ‘people who have a career/long-term job’. In my younger days I’d have taken this in a second, since I wasn’t planning on working at any one place for long, and was happy to do short-term contract work. Now I’m in an extremely stable job with good retirement benefits and plan to stick here for the long run, so it’s nowhere near as appealing. I think a lot of people who are working short-term jobs, jobs they don’t care about, low-end jobs (like most restaurant or retail jobs), and so on just don’t see any reason not to take it, while people in good jobs with long-term prospects will have a much harder decision. Also the question of whether the ‘year’s salary’ includes health benefits is a good one, paying CORBA rates for insurance for a year would cut down the prize quite a bit.
While $1 million would be nice, I don’t think I could retire on that. I’ve read estimates that you need more than that to continue your standard of living.
Further, the average full-time employee is putting in at least 50 hrs per week when you include commute time. Give someone an extra 50 hrs of waking free time per week, I’d bet they’d want to do things that cost money. IOW, there can be a big difference between ‘staying home’ & ‘not working’.
I’m not wasting any money on the infinitesimally small chance of winning $1 million; but the chance to be ridiculously, start-a-family-foundation, Mr. Moneybags rich? Yeah, I might throw down a buck or two, which ultimately drives more money into it.
It’s still a sucker’s bet but I’d be able to fund every fantasy I’ve ever had, cars, boats, planes, mansions (all plural). 
Don’t forget the high-end consulting jobs, IT & such. The majority of my cow-orkers are consultants, making above average income for the length of their part of the project. Roll off onto another one somewhere, rinse, repeat. Higher per hour rates but less/no benefits.
I can find a job any day of the week. Assuming I can eventually resign in the proper way, I’d do it without a second thought. If I just have to disappear, never to be heard from again, I couldn’t…too much legal trouble, let alone ethics.