Lego has made at least two versions of the Star Wars AT-ST and each has their own unique problems. The AT-ST (7657) is a Minifigure scale walker that is just plain ugly. Lego has also released an Ultimate Collector’s Imperial AT-ST (10174) which looks great but is much larger then previous AT-ST. It is way too large to display with Lego Minifigures. There is a great demand to have an accurate representation of the AT-ST that is appropriately sized to the Star Wars Minifigs. Over on Lego Ideas, user hobocamp has proposed a project for a fully posable AT-ST. The walker has a surprisingly large range of motion, thanks to its ball jointed legs, and is sturdy enough to stand on its own.
You can vote for the Lego Star Wars Posable AT-ST over on Lego Ideas: https://ideas.lego.com/projects/84533