It's true that if you play all your tickets in one drawing, you have a higher chance of winning the jackpot at least once, especially as your number of tickets approaches the number of total tickets. However, your expected value does not go up, because you lose the chance of winning the jackpot more than once.
For an extreme example, consider a lottery with only one number, selected from 1 to 2, costing $1 per ticket, with a $2 jackpot.
Buy 2 tickets at once, you lose $2 on tickets, and you get $2 back. Expected net return, $0 (with probability 100%).
Buy 1 ticket per draw for 2 draws, and you have a 1/4 chance of winning nothing (net -$2), a 1/4 chance of winning both jackpots (net +$2), and a 2/4 chance of winning one and losing one (net $0). Same expected value.
Of course, in a real lottery, usually[0] the expected value is negative. So what's happening is like anti-insurance. In both cases your expected value is negative, but you pay the insurance company money to lower your variance, and you pay the lottery money to raise your variance.
[0] Usually? Well, in theory with a cumulative jackpot the jackpot might get high enough to make the expected value positive... except that usually as the jackpot rises, the number of players rises too, such that you have to take into account the possibility of having the split the jackpot, which of course would cut your take in half, or worse.