Its because Newtek cheated! Same reason there never was a PAL Toaster.

All those fancy effects they did would normally require decoding incoming analog composite Video signal into RGB, sampling 3 channels, storing those 3 channels in dedicated framebuffer, having very performant effects engine juggling this huge amount of data around, then on the way out again encoding RGB back to Analog Video resulting in loss of quality. What Newtek engineers (Carvey?) did was a brilliant hack - Toaster effects are performed on raw undecoded NTSC samples. Amiga has no access to the capture framebuffer, its only used for UI and as a fancy graphical titler (like Sony HB-G900P MSX2 with built-in genlock, but much better). PAL video wouldnt work because every second line has inverted phase, shuffling raw samples would result in artifacts. PC wouldnt work because you still need Genlock and precisely synchronized 59.94Hz video output meaning now you need to build and ship custom Video card to replace whole Amiga.

That very same technique got reused on PC in 1995 by Paul Montgomery (Newtek co-founder https://en.wikipedia.org/wiki/Paul_Montgomery#Play_Inc.) in Snappy Video Snapshot LPT dongle. @TubeTimeUS on twitter did a Snappy deep dive, teardown and reverse engineering down to schematic and figuring out remarked "PLAY HD-1500" main chip is just a XC2064 FPGA. PLL + 30msps ADC + special 2Mbit video ram capable of holding whole field = this thing grabs whole one field of video all at once after perfectly synchronizing to 14.318MHz video clock. https://threadreaderapp.com/thread/1301990455182155776