Because non-humanoid robots require special accommodations
The colony you are building already needs to be designed for humanoids. A standard human staircase has 7.5" stairs at a 37deg incline which is hard for wheels to go up. So rover bots would need extra ramps or elevators installed to gain access to upper stories. We often build shelving and cabinets up to a heights of 7.5ft to maximize usable wall space which is easier to reach when you have a vertical body plan. Our standard doorways are 36" wide which is hard for something with a large flat base to get through. Our standard operating control interfaces can include a very wide range of widgets include knobs, handles, levers, switches, keyboards, triggers, buttons, latches, dead-mans-switches, plugs, etc... While many of these can be manipulated without a proper hand, they were all designed around human hands; so, the optimal appendage in almost every case will be something like what humans have.
... but these are just the every day things you need to reach...
Reaching the AC unit in my attic to restart the piolet requires first pulling down on a string that is 6ft in the air, then climbing a 75deg set of stairs to go through a 2ft wide opening that leads straight into the the low point of the roof line so you have to twist your body around as you come up the stairs to not hit your head, then you have to climb either over or under a 2ft high cross beam, step around the ducts so as not to crush them. Then you need to walk on other crossbeams because part of the attic floor is unfinished or you will step through the ceiling below, then you have to crouch down and hold down a knob with one hand and press a button with another to start the piolet light... yes, this space could be redesigned to be way more convenient than this, but it would mean more time, energy, and materials. Since my attic was only designed for occasional human use, a lot of corners could be cut and assumptions made knowing that no one was going to be running thier roomba up there.
No matter what body plan we choose for a robot, there will always be places that a Human Colonist can go that the robot can not... unless you give the robot a human body plan. So, by using humanoid robots, it means that you can design everything in the colony to be equally accessible to both robots and humans such that things don't need to be redundantly designed to accommodate both.