Also, the cheap options are using off-the-shelf upscaler chips that will choke on anything other than NTSC or PAL video baseband - the kind of chips that go into TVs that have retro inputs. As far as I'm aware there is no chip on the market that you can buy that will handle arbitrary analog video modes to the fidelity that we want them, and pretty much everyone is using some amount of FPGAs to handle some part of the conversion[0]. That's like half the BOM cost on these things alone.

[0] Don't ask me how much. I imagine you probably couldn't directly sample analog video on an FPGA.