I am as messy as some of these. In my case, I suspect I have adult ADHD, undiagnosed - was always this messy and struggle with things others find easy, like focusing and timekeeping.
My space isn't usually dirty but is messy.
Another factor to bear in mind is that space is a very expensive luxury - many families are crammed into tiny living spaces, through no fault of their own, and the reality is that there just isn't enough suitable storage for stuff, so it does end up piled in places, and piles fall over etc.
Particularly an issue for those living in rented accommodation, where it's not worth while buying suitable storage to fit the specific flat/house, because a) it's another expense and b) you might be moved on at any point at he whim of a landlord.
Many of these responses are unnecessarily blamy and judgy - having enough room to store your stuff, enough cupboards or whatever to do it in, and the ability/time to do it, is not a luxury everyone enjoys. Yes, people do get overwhelmed, particularly if they have young children who can mess up faster than they can tidy.
Having some empathy does not hurt. I know some people enjoy tidying. Understanding that some don't and find it difficult costs you smug people nothing. Bully for you. Bet when not mocking people who are messy, you are mocking people who fail exams or who are poor. 