I would, however, love that price point. It would be nice if I could run a few light-weight services on a VPS for $2.50 a month and then put my websites and other projects on a beefier VM.
I currently use Linode, but if DigitalOcean offered something at that pricepoint they would be getting $2.50 more from me a month than they currently do.
It's more about support costs if I were to guess. How many support tickets does it take for their profit on $25 a year to disappear? (if $2.50 a month is discounted to $25 a year).
ARIN charges for IPv4 address allocation (https://www.arin.net/fees/fee_schedule.html) and I read that below $5 a month it becomes unprofitable for hosting companies just because of the cost of leasing IP addresses. If your services can run on shared hosting there are a bunch of hosts for less than $1 a month around.
I currently use Linode, but if DigitalOcean offered something at that pricepoint they would be getting $2.50 more from me a month than they currently do.