I might not trust them 100%, but I trust them around 1000x more than I trust myself. I have had several data loss incidents and it was invariably my own fault. I simply cannot be trusted with my own data.

If one doesn't trust Google/Dropbox et.al. to handle the data, then just use two of them, or use a personal solution and one of them. Just don't use your home rolled backup system only because you don't trust any of the online storage providers.