If named individuals can be dead, named organizations can be disbanded or destroyed. Learning and using a dead organization's secrets and techniques is no different from learning and using a dead archmage's spells.
Technically true, but there are a few tidbits:
- those were new names, while spells names have a history from the earlier editions of the game; theoretically this implies nothing, but practically it does tend to transpose to the game world as well
- characters of the past die, they may be so special that they achieve godhood or similar, but the default is that after some time they're gone or at least so much beyond mortals that they are out of the game; organizations never really die, there's always the threat/hope that the evil/good group makes a comeback; this to me means that I an have spells named "Melf" and "Mordenkainen" in non-Greyhawk settings without the need to actually really have more than a vague memory that there were once great wizards with such names
- it just feels so much more natural to remember the names of the person who presumably invented the printing machine or the telephone, rather than the company they were working for
- I can bet that designers who come up with new organizations names will be very tempted to define such groups in some detail, and then use them in more places (prestige classes et al, or even published adventures) which will make them existing by default
- also, to keep the spells names short those organizations names needed to be so generic that they sounded more like taverns and hostels