Nobody ever seems to be able to pin down what exactly is so wrong though, besides the vague "showing off" and "you know it when you see it."
Take parenting out of it and put a similar behaviour into another context.
Most people when taking a phone call in public - have conversation at an appropriate volume for the situation, have no need to shout, end call. Nobody particularly notices or cares because it's just a phone call.
A certain type of (usually male) person who wants the world to know just how important they are - answers phone, speaks at fog horn volume, checks everyone is paying attention to him telling Dave that stuff needs mailing for the accounts, continues big important man work chat at full volume whilst everyone else wishes he'd stfu.
It's similar with parenting:
Most parents - talk to their children, engage with their children, have fun with their children, have educational conversations, use an appropriate volume for the situation. Children engage back in conversation. Good fun is had by all.
Performance parents - talk at normal volume until they feel something is noteworthy and then they switch to loud/annoying/over the top tone of voice for the very part they want people to notice, often end up doing some sort of cringe worthy narrative whilst the child looks at them like wtf/replies awkwardly or parent keep pushing the child to be a performing monkey. The people around couldn't care less and just want to enjoy their coffee, do their grocery shopping, or enjoy the museum with their own children and wish Annoying Mum/Dad would stfu.
The performance parent will see or hear people discussing this annoying pattern of behaviour and decide that everyone is hating on people just talking to their children, or that those finding the behaviour annoying are insecure, or jealous of more advanced children.