On top of that, the tooling is all proprietary, clunky, with obnoxious licensing. If you notice, that eval board you pointed to comes with "ISE® WebPACK® software with device locked SDK and ChipScope™ Pro licenses". I'm just not interested at all in any "device-locked SDKs".
And finally, there's a bootstrapping problem. FPGAs aren't really a mass-market platform, because no one has them (unless they're developing custom hardware).
If there are now $90 eval boards, that solves part of the problem. Another big step would be building a reasonable toolchain around it that does not consist of big clunky proprietary tools with onerous licensing.
And finally, someone will need to start shipping FPGAs with a standardized interface on commodity hardware. If I can depend on their being an FPGA in a phone, in a workstation, or in COTS server hardware, there are lot more possible applications. As it is, you already have to be building your own hardware before an FPGA is something you would want to target at all. The vast majority of programmers write code to run on COTS hardware (servers, desktops, mobile), not custom hardware.