One problem is, it would have to be permanent, once the steroids are stopped, the extra muscle will mostly fade away and the natural testosterone production will be inhibited, this is the worst effect, the people end up with a lower testosterone production than before.
But it's true, so long enough calories are given, they would gain some muscle, even without training at all.
An alternative might be hgh , but that comes with other issues.
Last but not least, all steroids are not equal, they're all testosterone derivates, the tablets are very toxic to the liver, and some derivates come with some more side effects than plain testosterone.
Science tried to develop a mild steroid with great anabolic effects , but all of them are not powerful without adequate androgenic properties. The androgenic properties is what makes a steroid strong and....causes most side effects and hormonal imbalances post going off.
To this day, testosterone seems to be the choice of medicine and by no means it's a weak drug, it simply upsets the body bit less as it's the same thing that the body produces.
There might be more points on why not give it to these patients, but that's the steroid side of things.