Bozak had a really bad offensive year last year. He's fine but not great defensively.
On the other hand - last year he was solidly above average defensively and not as bad offensively. Like solid middle-6 material, and not the worst if he steps into your 2C slot for a while or even longer if you have a bad team.
If you look at last season exclusively he shouldn't earn more than this. But there's a chance he regains form, and if not you paid nothing to take that chance.
Worst case you have an average 4C at 750k. Best case you have a solid middle-6 center for peanuts.
My guess why this took so long: If they were able to trade Tarasenko this summer, they would have been able to offer this all in salary as opposed to bonuses.
There's no benefit to giving salary over bonuses. I doubt the Blues would be waiting for that unless he was willing to take less money for pure salary. Hard to see that though considering this is already cheap for a 3C.