That’s a non sequitur. You aren’t likely to update the firmware on your hard drive to an open source version. You’re likely to update it to a newer vendor-supplied version (to fix power management or longevity issues). Similarly, the L5 modem vendor might come out with new firmware, which might improve idle power usage, fix security issues, or otherwise improve the modem’s behavior. Some of us might like to be able to use that updated firmware without needing a hot-air station.
As for not being able to make it free software legally… That’s not exactly true. It would only require the agreement of Broadcom and several other hostile-to-open-source large companies, and possibly the permission of the FCC and other hostile-to-freedom government agencies. Not likely to happen anytime soon, but remember, Microsoft itself released the source code for an ancient version of DOS, so stranger things have happened.