Amazon is big and it can get away with it. However, Amazon offers AWS and if I decide to run my VMs on there, it seems logical to store my data on Amazon as well, fewer compatibility problems, fewer pointing fingers in case something goes wrong and fewer different bills to remember to pay. As I see, if you use Amazon CloudFront CDN, then data transfered from S3 to that is free. And you probably pay less if you access the S3 stored data from a VM running in AWS.
Amazon also has service tiers - backups can use a slower, cheaper service while frequently-accessed data has to use a more expensive service.
There are a few problems with this, at least for a small company like Storj.
First, it may increase the price. Let’s say someone wants to back his files to to Storj. To do that, he needs to buy compatible backup software (there is no reason why it has to be free) and then pay Storj for the storage. This adds up to probably higher price than paying Backblaze for storage and getting the program for free.
Another problem is support. What if something goes wrong. It could be a problem with Storj or a problem with the backup program. The support of each may start pointing fingers at each other. I have seen this quite a few times, not with Storj, but in general.
A third problem is how to convince the developer to add Storj compatibility or make a program purely for Storj. Clients won’t really demand it because they don’t know what Storj is since Storj does not market to end-users. In comparison, pretty much everyone knows what Amazon is.
The developer probably does not have a reason to add it, unless he gets kickbacks (which would probably increase the price) and if he does add it, he will most likely just use the S3 gateway because it’s easier (if the program already supports S3 protocol), but it is more expensive for Storj.
Even if the developer adds it, now you still have to convince the end-user to use it instead of the other options which are probably supported by the same program. How? Leave that up to the developer to convince the user? Why would he do that? He already sold the program, it probably supports other storage services that the user uses.
For example, The “Hyper Backup” program on Synology NAS (why Synology? I have access to one) can back files up to multiple cloud services - Synology themselves, Dropbox, Azure, Google Drive, Rackspace, some others and even S3. So, in theory any Synology user can back his files up to Storj right now (using the expensive-to-Storj gateway of course, but whatever). How many would do it? How many know Storj even exists? Why should they choose Storj instead of the others? By the way, a random NAS user won’t need 5Gbps transfer speed, so he will either choose the cheapest option, the easiest option or one he knows best (“oh, it’s Google” or “well, my NAS is Synology, might as well use their cloud”).
Is there even a backup program for Windows that uses Storj? Other than the programs that only support S3 and need the gateway which removes on of the advertised features of Storj - end-to-end encryption.