Because now everyone who disliked Voyager and Enterprise thinks they’re great.
Oh wait, no.
I didn't watch DS9 much when it premiered. I thought the pilot was excellent, and then the next 5-6 episodes bored me to tears. I was in college and quickly gave up on it, only returning for really big episodes (season finale / premiers, "Way of the Warrior," "Trials and Tribbleations," "Far Beyond the Stars," etc). It got even harder to come back because of the serialized / arc nature of the show.
I watched it 1-n about 9 years ago when I got the full series on DVD and
loved it. Just completed a second full viewing this winter....loved it even more
ENT is almost the same story for me. I think I lasted about 4-5 episodes before I gave up, but then I virtually ignored it after that. I may have watched the Soong arc in S4, but that was about it. I fully watched it 2 years ago and thought it was a lot of fun and really enjoyed it. I actually feel compelled to do so again soon, because it's a relatively quick watch
So....yeah...it certainly does happen.
I think that when these series are watched further out of context, and further away from our ridiculous fan expectations, we have a way to enjoy them more for what they are, and we don't get caught up in all the crapola that clouds our ability to simply enjoy shit rather than pick the living hell out of it and/or get frustrated with it for really petty reasons.
Honestly, I rewatched S1 of Picard right after DS9, and there were many instances where I thought to myself "this is every bit as good, if not better than DS9." And, I liked PIC when it premiered, but didn't have really strong thoughts about it. Just on a second rewatch, less than a year after the premier, I was already thinking much higher of it.