Newsflash:
The world isn't a computer game that you boot up and start playing. The UK isn't some tinpot dictatorship formed a few years ago out of the ashes of French colonialism. It's one of the sources of Western government and politics and a mature political system.
You don't get to choose which bits you want, you have the bits that have developed. Britain has a Royal Family because that's the way it has developed over many many hundreds of years.
Like all these idiots that apparently "reject" capitalism. Hello? We didn't choose it. We developed it, and developed it because it works (albeit not perfectly), but the people that developed other systems have spent a long time in some pretty deep brown stuff.
Yes, Britain was a republic very briefly for about 10 years, and it was an unmitigated disaster with everyone hating the de facto "president" Cromwell, so much so that the monarchy was restored.