This is precisely because they compromised their principles with the AGPL that they didn't make it their main licence. They felt they had to let people make such a compromise, for some software.

The problem with software which have significant influence over the network is that it's "users" might not be the owners. Effectively, freedom 0 and the other three are in conflict. (My freedom to run the software is in conflict with your right to study it).

If I recall correctly, the FSF itself says AGPL software is not really free software.