it’s generally super weird how everyone tries really hard to convince you that you are wrong about it

My theory is that (volontary) childless people are less predictable to others. If you only have to take care of yourself, you need less resources (read: money) for that. An employer that knows his employee has children to care for can be treated worse in terms of working conditions and salary/ wages, because the employer knows that this employee can't afford to quit the job, because of the responsibility for the child(ren).

If an emloyee is known to have no children, it makes him unpredictable. He could get up after a good yelling at the workplace, say "fuck it" and leave. He only has to take care for himself. Also, that employee can accumulate more money since it has not to be spent on the needs of children. That means, the employee has a bigger and longer lasting financial cushion.

Something similar applies when credits/ loans have to be paid. Having debt is a considered a "good" thing, since people are less prone to quit their jobs. On a personal level, the goal should be to become debt free as soon as possible. Not only it will result in financial freedom, it will also enhance your "fuck-it-ablilty".

Another theory for those convincing people is that they envy your lifestyle of tranquility and spontaneousness. These people have been bullied into having children by their peer groups, because "that is the thing to do", and "you owe grandchildren". There are so many parents out there who would be better off if they never had children, but their relatives had convinced them otherwise.