You've got to think of the Monarchy as a much bigger institution than the (current) Royal Family.
To move to a republic from a constitutional monarchy is a big complicated project (the work of years if not decades). It's not just about retiring the House of Windsor. It's creating a whole new head-of-state system, detangling the monarchy from the legal system, armed forces, currency, government, historical buildings, land, new stewardship of current Crown properties etc. Will require a lot of money and effort to rework everything and deal with the historical legacy of a thousand year old institution.
Now that doesn't mean it shouldn't happen.
But for any political party to attempt that they are going to need unwavering support from the majority of the people, support for the cost and upheaval over many years, support for whatever head of state system is put into place. It's a process that will require thousands of different decisions in all sorts of different parts of UK life - some small and cosmetic, some big and tough choices.
Again it doesn't mean it shouldn't be done just because it will be expensive, difficult and take a long time. Once it's done, it's then done for good. We only need to do it once.
But if you think Brexit was divisive and a political millstone for both individual politicians and parties then this would be on a whole other scale.
You'd need a very strong, confident party in power with the assurance of a big majority of the country behind them to start and follow it through.
There are nowhere near the numbers for that. And while younger people are usually more republican than older people - the interesting thing is how more conservative (small c) people become when they are older. Even if a little momentum is kept with the younger people who currently have anti-monarchy sentiments to get to the type of majority which would be able to carry this through, you are talking many decades before that is viable.