1. This effectively poisons the well for any other BaaS providers out there. If two of the biggest companies in this space (StackMob and Parse) can get acquired and shut down in less than 5 years, what does that say about the future of the smaller companies in this space? As a developer how could you possibly trust any of these companies going forward, based on this track record?
2. Syncing is notoriously difficult to get right. Building a generalized syncing solution is even harder. Bugs in sync code tend to lead to data loss, which leads to angry customers. These types of bugs are hard enough to track down and fix in your own code. Trying to track down and fix bugs in complex third-party code can be damn near impossible.
If you decide to adopt a third party solution that purports to do your syncing for you, do your research carefully. Not just by looking at the toy samples which look easy to set up and work perfectly, but experiences and reports from actual developers who have tried such solutions. What kind of problems are they having? What are the limitations of the current implementation? How mature is the product? How responsive are they to bug reports? If something goes wrong and data is lost, how much insight do you have into the system to figure out why?