That, plus programming FPGA kind of sucks. The software tool chains are somewhere between 20 and 30 years behind the state of the art for software development.
Also, FPGAs can't be reasonably context-switched. Flashing them takes a significant amount of time, so forget about time-multiplexing access to the FPGA among different applications.
I could imagine some sort of API based queuing - say you have 2 "slots" you can program stuff on so if you play 8 k video you can have on flashed to video decoder while the other one can speed up your kernel compilation. If you then want to also use FPGA accelerated denoising on some video you recently recorded, the OS will politely tell you to wait for one of the other apps using the available slots to terminate first.
Since applications do all their rendering via the GPU these days, desktop multi-tasking requires reasonably time-sliced access to the GPU. GPUs have proper memory protection these days (GPU-side page tables for each process). That's big progress over 10 years ago.
