It's not TREK tradition. It's how tv is run.
In the 60s, there would only be about 8-9 minutes of commercials in an hour of television, which is why a STAR TREK episode is roughly 50-51 minutes long, when you add the trailer for next week and the end credits... which would actually air back then.
When TNG aired, tv had about 14 minutes of commercials per hour, having roughly 45-46 minutes of the episode, adding trailer and end credits... which actually aired.
DS9, the same.
VOYAGER, the same until their 6th season, which started to drop to 42 minute episodes, more often than not. Same with ENTERPRISE, which was all 42 minutes except season 1, if memory serves me.
At least, that's how tv has been in the US.
I have personally never been a fan of streaming shows, but the one thing I can say in its favor is that they are not constrained to the hour format of broadcast tv. Same with HBO, SHOWTIME, etc. FX and AMC are a little more lenient with some episodes, too... though they still mostly follow the current commercial-laden hour long format.
(I will say that my biggest issue with some DISCOVERY episodes, mostly in season 1, was that they SHOULD be longer than even STAR TREK ones were. Not fully taking advantage of the lack of hour long constraints just doesn't make sense. Not saying an episode has to drag, but you can add some minutes for just simple character scenes. DS9 found a way to do them and STILL work within the format. Streaming shows don't have that excuse.
Having said that, season 2 of DISCOVERY did improve on this, and I hope they continue to for season 3, and hopefully onward.)