It works for a while, but isn't a long-term solution. The win bonuses in Objective boosted the population for a few weeks, but it went down shortly thereafter (until this week, where the splash screen was from last month reminding people that Objective gave more credits, at which point the population went up to a whopping 1500). The super jackpot weekend they did a few months ago did almost nothing for the population. Also...
...this.
I think a lot of people here, for a long time, have been advising them to make the game they want to make and not try to please everybody. Trying to please everyone made Reach's situation a mess with the TU split, and I don't think anybody wants a replication of that problem.