This is answered by the GPL FAQ on Tivoization (quoted below), which applies to LGPL too.
The LGPLv2 and GPLv2 requires source code and the means to recompile a modified version of the software to be made available to those who received a copy of the software. However, it does not require the software to be updateable into the device. Updating the software into the device is typically prevented using Secure Boot, because the end user would not have the signing keys.
The LGPLv3 and GPLv3 introduced new conditions in Section 6 to require that the end user of a consumer product must be able to receive the signing keys and update the software into the device.
Due to this, to be on the safe side, many embedded product manufacturers ban the presence of any software licensed under GPLv3, LGPLv3 or AGPLv3 on their products, regardless of whether it is a consumer product or not. Secure Boot is necessary for ensuring security and safety of the product, while preventing violation of product liability and loss of warranty.
Linus Torvalds strongly disagreed with the anti-Tivozation clause, and hence licensed the Linux kernel under GPLv2-only.
What is tivoization? How does GPLv3 prevent it? (#Tivoization)
Some devices utilize free software that can be upgraded, but are
designed so that users are not allowed to modify that software. There
are lots of different ways to do this; for example, sometimes the
hardware checksums the software that is installed, and shuts down if
it doesn't match an expected signature. The manufacturers comply with
GPLv2 by giving you the source code, but you still don't have the
freedom to modify the software you're using. We call this practice
When people distribute User Products that include software under
GPLv3, section 6 requires that they provide you with information
necessary to modify that software. User Products is a term specially
defined in the license; examples of User Products include portable
music players, digital video recorders, and home security systems.