Odds and lines differ between sportsbooks because they are all running businesses where their odds are set so as to generate a profit for the sportsbook.
So if, for example, one operator has accepted multiple high-value bets on one specific sporting outcome, they may drop the odds to limit their losses. Equally, they may offer higher odds than another sportsbook as an incentive or even a loss-leader to gain extra customers. These are just two examples; there can be multiple other reasons for differing odds.