Even Netflix and Disney+ do not have that. The TV also takes some time to respond.
And on my TV Netflix manages sub-second (at least sometimes). IDK how. Maybe they somehow give me the DRM keys ahead of time? Maybe everything in the "continue watching" is pre-approved? Maybe the first couple of seconds are handled differently, maybe they are not DRM protected? Maybe the netflix intro logo thingy is cached locally, and then stuff happends in the background? It is after all more pleasant to hear the intro sound that watch a spinning loading-thingy. Maybe as I move the selection across stuff they pre-emptively fetch the first seconds? In some cases it also seems to start auto-playing in the background, so the only thing that happends when I press a selection is that the GUI overlay dissapears.
Because the content owners demand it. No content = no customers. You could probably build out a public domain streaming service, if you really wanted to build out a non-DRM streaming platform, but it's going to be hard to find customers for that too, I'd imagine.
1: Every customer wants their own twist. It is not enough to create an awesome video player app and reskin it, no they all want to be special.
2: Getting the last 5% takes twice as much work as the first 95%. Probably even more.
It's quite doable for 'normal' engineers to make a steaming platform. You need to get the video files out there on some CDN, you need some service for the DRM keys (which needs to scale, and handle the different access packages), and you probably want some history and profile stuff. Easy enough. But for the best experience you want every video to start playing in less than a second. That means getting those starting video segments as close as possible to the customer, it means optimizing that DRM key delivery, and optimizing the player so it just gets that video pushed to the screen ASAP.