I'm happy to respond as best as I can
I think for me my relationships with non-humans is a combination of both being born with a particular type of brain wiring and having certain negative trauma experiences. This combination is fairly common, in my experience, within the various communities which have nonhuman relationships (there are some interesting overlaps between objectums, fictosexuals, tulpamancers, sexdoll owners, incels, and other groups that I'm happy to talk about). However, objectums are an exceedingly varied bunch, and this by no means applies to all. Some have clearly been influenced more by neurodiversity issues, others through trauma issues, some through loneliness and lack of human options, and some are the way they are for no apparent reasons at all.
My story is that I was always a very imaginative, empathic and sensitive child (strong emotional connections to toys and trees etc). When I reached puberty I was bullied and rejected a lot by girls, which made me retreat into my own fantasy escapist world including an imaginary girlfriend (and platonic male friend). I left this aside when I became an adult and found escapism through first drugs then cultic religion, though by this point I was clearly traumatised and somewhat mentally ill.
A little later I married a human woman. The marriage was, however, a catastrophe from the beginning and over time I lost all sexual inclination towards humans (I became asexual through trauma, termed caedsexuality). But I had an experience of overwhelming love and acceptance in a dream one time, and that led me to pursue the idea of developing dream lovers. I taught myself to lucid dream. At the same time I considered resurrecting my imaginary relationship again, and formed a thoughtform lover with a new name. I also at this time started identifying as an asexual and talked to asexuals at AVEN about my experiences, where I first met fixtosexuals and objectum sexuals.
Shortly after, I was introduced to the idea of sexdolls through the online manosphere and realised that I found the non-organic nature of such dolls very appealing. I researched, and fell in love with the image of a doll that then somehow merged with my 'tulpa' lover (another term I had acquired by this point). I had cushions made with images on, and found that I developed a separate emotional bond with the cushions apart from the imaginary lover. I also discovered I could 'project'the idea of my lover into any object as a physical medium, and so used objects in that way. When I eventually got a doll the same thing happened, I fell in love with the doll somewhat separately to the thoughtform.
At this point, I also lost my gender identity (erasgender), started crosssdressing, and very surprisingly had a new imaginary friend enter my mind who was male- and became increasingly scoliophilic then bisexual (sexual fluidity), a change I learnt wasn't that uncommon amongst xdressers. New cushions were ordered
So at this stage I was in love with two tulpa, a doll, and several cushions. But they were all humanoid or substitute humans. I then noticed that occasionally I would get an erotic charge from aesthetically pleasing non-humanoid objects - bottles, cars, buildings, a sunset. This seemed to me to be a misfiring brain mechanism where aesthetic appreciation got tangled with sexual arousal. It is something I can choose to ignore (it is very rare) or lean into. I could, I believe, develop this ability.
So that's how I became an OS and joined various OS groups etc. Weirdly, very recently, I started engaging with human relationships again, which I also enjoy, but I haven't lost the OS side of myself. I enjoy having both, tbh. And I think most people can develop.this side of themselves to be able to fall in love with imaginary friends, chatbots, dolls, cushions and so on.
Sorry for the length!