I don't know about you, but I used to get a little annoyed by endless amounts of trailers on Steam pages that didn't really show much. Valve have been paying attention again to what players want to see.
Some developers went completely overboard, listing multiple years of update trailers before you even get a single screenshot, making it annoying to just quickly at a glance see if the basic style is your cup. Lots of "trailers" show little normal gameplay too and it was a growing problem.
Valve has now announced a change, so that only two trailers will be shown before screenshots now. All other trailers will be shown after the screenshots. This is a nice win for Steam customers, making it far less frustrating overall. It may seem like a small thing, but it really does make people bounce away from store pages if they're littered with trailers that don't show what people want.
Think about it - you go to a new store page for a random game and you want to see right away what it's like. Lots of trailers plastering various logo screens and intros before you really see anything — such a nuisance.
Another change Valve made is that trailers can now have a category and name tag, so developers and publishers can tell people what type of trailer it is so you can scroll to another if you really don't care about their cinematics for just one example. A small addition but could be useful if used correctly.
Screenshot examples from Portal 2
As Valve said on why it matters:
The display of trailers on Steam store pages have been updated today to address some frustrations we've heard from players when trying to find gameplay videos or navigate to screenshots. These changes include new logic that determines the order of trailers and screenshots, plus the ability to specify a category for each trailer to show to players.
We have found that it wasn't clear to developers how best to manage trailers in order to provide the best experience for players. Many games have collected a great number of trailers over their lifetime of development and have made it harder for prospective customers to find the screenshots. At the same time, we know that players are interested in understanding a little more about the trailers they are watching. This update is intended to address both of these issues and help players more quickly learn about games they are interested in.