I question heavily the economic factor, given how many kids people had in the past when they were dirt poor. It seems more common that the wealthier you are, the less likely you're to have kids - until you reach a certain level of wealth, then it's kids time again.
So, I have no interest in having kids in general because a) I don't like them and b) I know my impatience with them would make me a terrible father, but as someone who fits into that middle-class comfort zone I can empathise with why someone in my situation who did want kids would still think twice about actually going through with it.
It's mainly just the day-to-day quality of life. It's easy enough to cover your own costs and possibly cover a stay-at-home housewife's costs too if you get yourself a not-shit job and are sensible with your spending, but if you bring a kid into the equation you're probably gonna both have to go to work, likely full time, meaning you barely ever get to spend time with the kid anyway.
That means it won't be you bringing him up, it'll be the school. Most people aren't going to be able to afford the fees for a good private school so they're dependant on the state schools which decline in quality more by the year, where the kid will be exposed to influences a self-respecting middle-class parent wouldn't want their kid to be exposed to. State schools are full of chavs, non-English speakers, and other troublemakers; and generally have a social culture that punishes aspiration rather than rewards it.
The problems won't even be over when he finishes school for the day; you'll still be at work for another few hours so he'll get dumped off with either a childminder or at Grandma's place long after she thought she finally had some peace and quiet, which in itself places a burden on either your wallet or your extended family's time.
You're in a situation where you're working all day, every day, to cover the cost of living. You barely see your kid, you barely see your wife, your house is a shithole because you're never home to tidy it up, you're eating slop most nights because you're not at home to cook. It's not an issue for the wealthy because they have the means to avoid most of these problems, and it's not a problem for benefit claimants who can stay at home with their kids all day courtesy of the taxpayer, but for working and middle-class families who're just trying to get by, raising a nuclear family in the current year sounds fucking miserable.