JizzyJiz -
Sadly, this is incredibly common. One of my departments runs the soup-to-nuts process of documentation, enablement and manual creation for products - it is a huge effort when you have a mass-produced product. That isn't to say your point is valid; there are many ways it could be argued that effective documentation can help reduce product returns, warranty claims and even FTC consumer accidents/complaints (at least within the US).
For a product like these drones, you have to factor in localization costs as well as legal. In many states the manual is, in fact, considered a form of contract or agreement of understanding that can also leave the corporate entity culpable if not properly written (eg. insufficient formal notices, scenario based examples, etc.)
Also keep in mind the infancy of the software and the frequency of the updates, dramatically adding to the effort and cost. One of our clients was a just-launched security cam company, each software update cost around $9-12k for documentation rewrites that included reprint of physical material for in box physical product plus web-copy updates and PDF updates.
As a consumer it's totally annoying, but from the back-end, I completely see why it doesn't happen. Luckily, with hobbies such as this, there is an inherent parallel to web/online sharing that accompanies the purchase/use of such a device (for example, this forum!) - this often helps soften the need for official/thorough documentation from the manufacturer and, in some cases, creates justification for them to not throttle-up effort.