benefit of using AWS cognito sync rather than user profile in dynamoDB

I'm starting out with mobile AWS and came across the AWS Cognito Sync service. I wondering what benefit this service offers over storing/fetching a user profile from dynamoDB?

In terms of complexity, maybe sync is slightly easier to use? but not much from what I can see.

Cognito Sync collisions are probably rare, and using dynamboDB with 'last write is right' is probably a good enough similar solution.

I'm struggling to compare on a cost basis, but to me it seems like 1 million reads with sync would be ~$15 a month, and with dynamo I could have 1 million per day for ~$7.50 a month. So 60x cheaper? Although I would be happy to pay either with that many users :)

What am I missing that makes this service worth using?

cognito pricing

dynamoDB pricing