I am really sorry that you tested positive after the cruise. We were on the same cruise and it wouldn't surprise me if more have also tested positive since disembarking. With the captain announcing that there were 19 cases on 9 June and then announcing on 12 June that there were more cases but didn't give a number, I suspect that Covid cases may have been higher than we will ever know.
We also had a fabulous cruise but unfortunately not everyone did take precautions. During our shore excursion in Kotor we were the only people on the bus wearing masks. We also noticed that about 75% of passengers waiting in the theatre for their shore excursions did not wear masks, unlike when everyone wore masks and socially distanced during shows in the theatre. There were many people coughing and sneezing towards the end of the cruise who were not wearing masks, including on the shuttle bus in Livorno. Of course there were also risks in picking it up while on shore.
It is such a shame that you took precautions and still ended up with Covid. I hope you recover quickly.