Because video has to capture, process, and store every frame in real time. A 33MP frame at 24–30 fps means reading huge amounts of data continuously, which increases cost, heat, power use, processing demands, and storage needs. Doing that at 100MP per frame is far more difficult than taking a single 100MP still.

Still photography has different priorities. A still image can be captured once, buffered, and processed without needing continuous high-speed output. Extra resolution is useful for:

• large prints
• heavy cropping while keeping detail
• preserving fine texture and detail for post-processing

Video and stills are also viewed differently. With video, motion, timing, and sequence often matter more than extreme per-frame detail. With stills, viewers may examine one image closely for fine detail.

So it’s less that manufacturers “prefer” high resolution for stills, and more that very high-resolution video is much harder and more expensive to deliver practically, while high-resolution stills provide clear benefits for some photographers.