Some people can deal with particular health conditions (or mental health conditions), others cannot

For example: someone who is completely blind. I did date someone (before I was disagnosed) who was completely blind) but my then-undisagnosed mental health and learning disabilities, meant that sadly we could not move past everything to continue to date each other, its nothing against people with any disability, just that sometimes someone cannot cope with one disability

Better to find out sooner, rather than years down the line when you are married and have 2 kids and a dog and a house and whatever else