AFO gives quirks and steals kids but all this time just ignores Izuku, Garaki was Izuku's doctor, a perfect quirkless boy that easy could turn in a nomu or anything but he just left Izuku goes. At this point dfo is the only good explanation for all this.
I wouldnt say he "steals" kids. Its more like he takes abandoned children nobody wants in (tomura, touya, chisaki and other orphans), but he gives them to babysitters (kurogiri, the doc and that creepy sunflower guy in chapter 350), because he clearly doesnt care about them and feels zero attachment for them. I saw posts about afo being a terrible father to these kids, so izuku should be glad not to have him around. But people seem to forget that afo DOESNT have father feelings for this children. All of this children are tools for him and nothing more then lab rats, vessels for his quirk if something happens to tomura. As soon as he doesnt need them anymore they end as noumus (Im looking at you little tsubasa) or dead. He isnt a father figure for them and it seem like as if he never was part of these childrens life except tomuras. And even with him he mainly interacted with through a computer monitor. So fact is, we still have no idea what kind of father afo would be to izuku. He could geniusly love izuku and be a good father to him before he left "overseas".
And yes, the fact that izuku is the only child afo and garaki ignore, despite being the perfect test object, is pretty much one of the biggest dfo hints so far. Afo doesnt care about if these children have quirks or not, look at aoyama. He gave him a quirk and from then he and his parents had to work for him. Even if afo was not interested to use izuku as a vessel because of him being quirkless, he could have used him for something else. He isnt picky when it comes to using people for his own gain. An other fact that is also still sus is garaki not talking about or mentioning izuku at least ONCE in 349 chapters, despite knowing that he is the current ofa holder and the only person that could stop afo and tomura. As if he was ordered never to talk about him no matter what.
Also we need to ask ourselfes the question, if dfo is true (and you are absolutely right anon, it IS the only logical explaination) WHY did afo fathering a child and MARRY a woman, when he already has like 30 back up kids in his storage, that arent even his own? Also the timeline makes clear that afo took tomura in when izuku was already born. His son was between a few months and a year old, but he STILL decided to use an other child/ren for his plans. And at that age it was impossible for even garaki to find out if izuku has a quirk or not.
So to me garaki telling that izuku is quirkless was because of 3 reasons. 1. Izuku ISNT quirkless (enough hints in the manga) and he has a version of his own afo quirk (again enough hints) 2. At the age of 4 little izuku was already the biggest all might nerd in whole japan and has already decided he wanted to become a hero just like his idol. Pretty sure that was a BIG thorn in afos eyes and it reminded him of an other family member who was obssessed with heros and turned against him. And 3. Hoping that growing up in an anti quirkless society, shunned out by all the other people and treated like "worthless and useless" trash (well done bakugou *sarcastic*) would change izukus world view and make him start to hate hero society, so izuku will follow him willingly when the time comes and not rebell against him like yoichi did. But that completly backfired, because izuku still wants to safe people, no matter if they treated him like shit or not. And thats the reason why afo is still trying to make izuku see the flaws and fuck ups of hero society by sending people like nagant after him.
Sorry my answer got a little bit out of hand 😅, but thanks for the ask anon 😙