Except it's GPLed, so it can't be used in any closed-source apps, or any apps that you want to distribute on the App Store, without an explicit exception.
If you're not married to the license for philosophical reasons (which I would respect, it's your right), I'd suggest a change to something simple like BSD.
This would, of course, allow someone to take your code, change it, and not release their changes, but it would also make it usable to the majority of programmers.
>.."distribute on the App Store, without an explicit exception".
Otherwise, my goal with using GPL is to preserve the concept of copyleft with the library. The GPL only applies if you plan to distribute libzdb to third parties. In that case, my hope and the reason I use GPL is that any modification done to libzdb can be contributed back so others can benefit. Otherwise, you can do whatever you want with libzdb without any restrictions.
For instance, I can't find anything on the website that would explain how to submit a patch. There's a mailing list and it'd be great by 2002 standards. Hosting this on GitHub (or any other site with a forking workflow that's just as smooth) would probably solve your problem without having to resort to imposing legal restrictions. There still would be a few companies/people unwilling to help but only a considerable minority.
The LGPL requires that the end-user be able to replace the library with an API-compatible library and still run the program. That's arguably impossible with an iOS device, and certainly impossible if you don't provide at least object files that can be relinked. Even with object files (or source) they'd have to pay to register as an iOS developer.
I suspect the majority of developers using the LGPL don't realise, or perhaps even agree, with this intent, so you're probably unlikely to be sued, but it's what the license demands.
If the author wants to use a GPL license, its his decision. But using a viral license in a support library is harmful in any case, as it destroys all ability to use it in a program that incorporates other pieces of code that might not be compatible with the GPL.
This isn't news; this requirement exists on all platforms, not just iOS.