That IC says: Support for DC- and AC-Coupled Input Signals
This:
Analog Input Clamping
The TVP7002 provides dc restoration for all analog video inputs including the SOG slicer inputs. The dc
restoration circuit (a.k.a. clamp circuit) restores the ac-coupled video signal to a fixed dc level. One dc restoration
circuit is implemented prior to each of the three ADCs, and a fourth one is located prior to the SOG slicer. The dc
restoration circuit can be programmed to operate as either a sync-tip clamp (a.k.a. coarse clamp) or a back-
porch clamp (a.k.a. fine clamp). The sync-tip clamp always clamps the video sync-tip level near the bottom of the
ADC range. The back-porch type clamp supports two clamping levels (bottom level and mid level) that are
selectable using bits 0, 1, and 2 of register 10h. When using the fine bottom-level clamp, an optional 300-mV
common-mode offset may be selected using bit 7 of register 2Ah.
In general, the analog video input being used for horizontal synchronization purposes should always use the
sync-tip clamp; all other analog video inputs should use the back-porch clamp. The advantage of the back-porch
clamp is that it has negligible video droop or tilt across a video line.
sort of says why AC is preferred. It can DC level the inputs.
Then within the datasheet it says AC coupling necessary.
Then see:
https://electronicdesign.com/analog/get-grip-clamps-bias-and-ac-coupled-video-signals
The short answer is it's required by government regulations.