They are relicensing from LGPL to MIT.
MIT is a more permissive license, which obviously appeals to some people.
I believe one issue in particular is around static vs dynamic linking – you can use an LGPL library from non-GPL code (even proprietary code) via dynamic linking, but LGPL only allows you to static link if all code in the executable is under a GPL-compatible license.
Okay, maybe that isn't technically true – from what I understand, the LGPL will let you statically link LGPL code with GPL-incompatible code, provided you either (a) make the GPL-incompatible code source-available, or (b) at least ship object files for the GPL-incompatible code so the end-user can relink the executable. The point is that the LGPL requires you to make it possible for the end-user to modify the LGPL bits, even if they aren't allowed to modify the rest of the executable. But, many people don't see these two approaches as acceptable.
> But, many people don't see these two approaches as acceptable.
why's that? I don't see the issue myself.