That's because that's all the Apex has ever been capable of. To get a true progressive stream you'd to stream the video through something like an rmtp or hls server and may even need to re-encode it depending on the webcam you use.
The Apex "stream" is nothing but a few snapshots every second, like the stuff we used back in the 90s for commercial cc video surveillance. They don't have a choice but to use that, otherwise they'd need a hardware encoder for compatibility and a progressive streamer built in, that's not going to happen.