Could you confidently draw the same conclusion if a person was operating the mower? Suppose that the neighbor's kid agreed to mow your grass on Saturday while you were running errands and it wasn't done when you got home. Would you have to conclude that the mower (yours or his) was either stolen or malfunctioning? No. There are a whole host of other possibilities when a person is involved. That is especially true if his mower has been proven to be reliable and reports of theft in your neighborhood are basically non-existent. He may have a legitimate reason for having missed his appointment.
It seems to me that a lot of objections raised against God make the mistake of approaching him as a machine rather than a person. If a machine does not do what we expect or want it to do, then it is either broken or missing. However, if a person does not do what we expect or want them to do, that does not necessarily mean that they have died (or never existed), or that they did something wrong. Don't misunderstand me. I am not suggesting that God, like an imperfect human person, makes commitments and then, for whatever reason, fails to fulfill them. Nor am I suggesting that he acts capriciously. What I am saying is that God is a person, not a machine. Thus, when he does (or did) something that doesn't comport with our expectations or desires, we cannot take him apart and pinpoint the faulty component. Nor can we simply say that he does not exist because he isn't doing (or hasn't done) what we want, when we want it, and how we want it done. We can do that with a machine, but not with a person.
The way to understand why a person does what they do is not by dissection, but by revelation. You could run a hundred physical tests on the neighbor's kid, and barring some sort of major injury or illness, you would not have any clue why he did not mow your grass. He has to reveal the reason to you. The same is true with God, and has revealed a tremendous amount about his character and his motivations through Scripture. However, he has not revealed everything that we might like to know. For example: Why does he choose to allow evil to exist temporarily? We can speculate based on what we know. And critics are free to use what we know to say that it is unlikely that God exists given the existence of evil. However, to insist that he necessarily cannot exist or is dysfunctional is treat him like a machine--to assume that he could have no reason for doing so. Someone might even go back a step and insist that if God exists, then he is obliged to reveal to us everything that we want to know. But here again, we err when we insist that his failure to do so serves as proof that he either doesn't exist or is "broken." He is a person, not a machine.