These companies usually bring something really easy to use, let people onboard and modify their network/DNS/etc to hell until they get vendor stuck and then they squeeze every possible dollar out of their pockets. Once you're in, after days or weeks of fine tuning, after you managed to pollute your codebase with their configs and IP addresses, it's hard to get out.
I suspect those "free slots" will change soon ,but we won't see those types of graphs anywhere soon and be prepared to get charged for bandwidth and everything else possible.