So far, I have never seen any article or even comment online explain explicitly why this is the case.

Almost everyone can see quite visibly that crime is not decreasing but then you have people with a clear political and financial motive saying: the stats, you are just a loon or (even worse) someone who might not be from London.

If you read the best source on this, hospital admissions, you will see that ~95% of the drop in "violent crime" is due to decreases in alcohol consumption. That is it. Ex this impact and in relative terms, violent crime in cities has been increasing significantly. And violent crime is supposed to be the rare subset of crime when, obviously, other categories of crime are generally increasing.

Btw, the group that publishes this data is also (strangely) unwilling to make this known and, afaik, do not include this information in press releases.

The other factor is that the composition of London's population has naturally changed over the last ten years. As London has continued to dominate economically, the poor have been emptied out from certain areas contributing greatly to a reduction in crime stats (and, unfortunately, an increase elsewhere in the country). For example, Camden has seen a huge reduction in violent crime, is this a surprise? If you look at areas that have stayed the same, crime has got worse (again, in relative terms/ex the above factors, crime in the UK is falling in many areas and rising in others).

I will say this another way: data is not collected fairly or accurately. There are massive political and financial incentives against accurate data. In London, this has always been the case because it is not possible to win elections in some areas in London with high crime if you admit that crime is high in those areas...you have to blame society. Twenty years ago, you had the same thing: city has never been safer, politicians doing so well, Met doing so well...once you have seen this a few times, you should start to wonder whether it is true...particularly as the current line is that crime was rampant twenty years ago...when it obviously wasn't. Anecdotes will always tend to represent the reality better than data which is produced for political purposes (and I think people know this, the stats exist in part so that people can hop online and say that everyone is doing a great job, you see the same thing online with central government...it is very weird).