Are you sure it's a movement from criminals focused in crypto adopters only, and not in wealthy individuals in general? Because crypto is money like any other currency and what differs one person from another for the criminals is how much they possess. So we could investigate it further in order to find out if it's not just a general security issue in France, where criminality rates in general could be rising exponentially against other groups of society as well, going beyond crypto adopters.
I believe crypto users specifically are being targeted due to the irreversible nature of crypto transactions. There is also the mistaken assumption among criminals that crypto transactions are untraceable. However, if crypto becomes a bigger part of the traditional finance world - which is likely - these kidnappings could increase and non-crypto people may end up getting targeted. So governments need to develop countermeasures to prevent kidnappings from spiraling out of control - for now it's out of control in France. The French government is on trial so to speak - if these attacks continue, the voters will throw out whoever is in charge, because it's embarrassing for the nation.