There are certain basic skills a goalkeeper has to master at the basic levels. They include: catching, diving, distribution, playing with the feet, stance, and positional play. I'm excluding here higher level stuff like tipping over bar or extension diving. This is the basics. At age 10, their bodies simply aren't wired to do it and they don't have enough training to successfully execute it. Yes, you can have a superathletic kid that does a good job at one particular aspect of the play....that doesn't make him elite because they don't have the training. A reputable GK trainer won't even start training a GK before age 8/9...there's no point....they can't safely execute the very basics of the moves without hurting themselves. And at U10 the expectation really should just be try and block the stuff that's shot right at you.
I am frequently amazed at how constrained your view of the soccer world has been.