My guess is we’ll see continuing unlimited offers coming. You can get a 1 TB disk for $50 retail; in bulk, probably less than $40 each. That 25 GB storage is just $1 cost for HDD.
They’ll make money on ads or selling you services - like Microsoft offering unlimited storage for their music and productivity tools. Use their tools (pay money), they’ll toss in storage online for free.
That's for the average desktop hard drive. I don't know whether cloud storage uses that or the more expensive (but reliable and faster) high availability drives.