Yup, the long term signup deals are specifically to reduce churn, which is shaping up to be the biggest challenge for streaming services. Disney don't want you to sign up for two months, binge watch everything, then cancel; so they're offering a carrot.
For me the math on the D23 deal made a lot of sense. For others being free to do say: four months of Netflix, four months of Starz, and four months of D+, might work better, and that's why I expect to see other services adopt a few of D+'s tricks, namely discounted commitments, and staged episodic releases for shows.