In the early days of streaming, content owners only had what they had sitting on the shelves. Most of those were SD masters that were formatted for broadcast. In the US, that meant 30i sources. Most TV was shot on 24p film, transferred to 30i in a telecine, edited without any regard to that film cadence, and that was that. The opening/closing songs were typically cut from that same footage, and doing an inverse telecine on that content was a nightmare. Everyone of us that dealt with that to supply the early days of streaming content had "so much fun".
Content owners suddenly had a vested interest in making their content look better, and now there's a way to get compensated to have better sources made to provide to those streaming platforms. To find the original film from old SD TV shows would be very rare. Feature films have been scanned from negative many many times. I was part of scanning a studio's entire library to HD. They've since gone back and scanned (or are scanning) again for 4k. Each time the scan is done, money is spent (and it's not cheap).
Now, the streaming platforms have the clout to refuse "subpar" sources now, and can demand that these restorations are the preferred source
Content owners suddenly had a vested interest in making their content look better, and now there's a way to get compensated to have better sources made to provide to those streaming platforms. To find the original film from old SD TV shows would be very rare. Feature films have been scanned from negative many many times. I was part of scanning a studio's entire library to HD. They've since gone back and scanned (or are scanning) again for 4k. Each time the scan is done, money is spent (and it's not cheap).
Now, the streaming platforms have the clout to refuse "subpar" sources now, and can demand that these restorations are the preferred source