I agree with you, in my experience, the parents who say having more children is so 'easy' are one of the following:

1. Deluded (lying to themselves because the truth is too scary).

2. Pretending (playing 'happy families').

3. Don't care very much and content to 'wing it'.

4. Not sensitive and can take a large amount of stress/punishment.

5. Have extremely chill children (rare).

6. Have a huge amount of outside help from Grandma etc.

Having kids is fucking hard, anyone who says otherwise is suspect.