The old format I felt were very unique.

Frankly, this is a huge misconception that just doesn't reflect reality and history.

The old format of Star Trek was not unique. It was emblematic of popular TV of that era, which was typically written with syndication in mind, so essentially all television was episodic. The main thing Trek did a bit differently was focusing mostly on "morality play" storytelling, but even that was not exactly uncommon.

TNG was an episodic series because that stood to make the most money, both because of syndication (which the show was designed for from the start) and because it meant they could buy one-off scripts from freelance writers which is cheaper than maintaining a massive writing staff.

It ended up working very well for the kind of series they made, but it was not fundamentally an artistic decision or even a choice that was special to Star Trek. It was simply the only way to get the show made.

If you took the exact same people and put them in today's TV landscape, they'd have made it serialized because that's what makes money. And yes, that includes Gene Roddenberry; at the end of the day he made TOS the way it was because he thought it would make money. He even explicitly mentions this in the writer's guides and other contemporaneous primary sources.