It's not so much the upload, but the fact that it will always be unclear (and dynamic) what this service will do with a particular LOC. You might store sensitive documents in Google Drive, but it is unlikely you will type something sensitive into Google Search. Because it is a smart autocomplete feature, there will always be lack of clarity of when they delete your files, if at all.

Github and PaaS do not have any direct benefit of storing my lines of code forever. There is no logical comprehension of doing so. If they are caught, they will lose customers forever. In a service like this, however, it can always be claimed that the storage was done in order to make the service smarter. Which would be true. But it would be dangerous.

It is also worthy to note that this is a live tool. With other services, one has a chance to clean their code before upload. With this, even playing around with an API with embedded keys in your code has already put you at risk.