Based on spending months in Barcelona, pickpockets still are an issue in the city. Anywhere that tourists congregate in Barcelona — on La Rambla walking street, in front of Sagrada Familia cathedral, on the beach in Barceloneta, and in the metro, for example — pickpockets inevitably are at work.
Of course, this is not a problem only in Barcelona; it is not uncommon in other locations that also have a large number of tourists. Barcelona is one of my favorite cities — it certainly is one of the world's best for walking — but it also is a statistical reality that there are more pickpockets in Barcelona than there are in plenty of other places that also have many tourists and people.
The reasons for pickpockets in Barcelona are numerous. It is a largely affluent city with pockets of not insignificant poverty (El Raval, for example), receives millions of tourists a year (including tourists from cruise ships that may only be visiting the city for a few hours), and Spain has long had very high unemployment rates.
Perhaps most notably, though, the historic penalties for getting caught as a pickpocket in Barcelona were negligible (theft less than €400 was barely a crime). There reportedly was a change in the law this summer to make prosecution of repeat offenders more likely, which may help, but the statistics have not changed much yet:
According to police figures, between January and the end of May this
year there were 34,000 thefts reported in the city, around 225 per
day. So not quite the 12 per hour of 2018, but not far off, averaging
just over nine per hour.
By comparison, London has roughly 127 reported pickpockets a day and it is a much larger city. It might not be fair to label Barcelona the pickpocket "Capital of Europe" — a lot more data would be needed to really verify such a title — but it definitely does have a lot of pickpockets.
Although Covid substantially reduced cash usage around the world, southern Europe still has much higher rates of cash use than northern Europe — 53% of transactions in Spain are in cash — so there still is plenty of cash that can be stolen in Barcelona.
Payment cards, passports and IDs, jewelry, watches, personal electronics, designer bags and luggage itself also remain targets of theft. Cards commonly can be used for some small transactions before being disabled. Identity documents can be resold and often combined with stolen online information for identity theft by transnational crime syndicates. Jewelry, watches, designer goods, and at least some personal electronics still have plenty of resale value in the hands of sophisticated criminals, as well.
If the risk of a penalty is close to zero — as it long has been for being a pickpocket in Barcelona — the reward is greater than zero, and the alternative very well could be unemployment (zero), it doesn't take much of a return on investment for an activity to continue.
It is best to keep the answer specific to Barcelona — and the areas mentioned are the most precise advice that can be provided — but to protect yourself, not carrying much in the way of valuables is a good first step. It also is smart to not wear flashy clothing, jewelry, or watches and be aware of your surroundings and cautious of your belongings regardless of their value when in Barcelona.