Privacy

I'll note too that even absent Heritage Foundation threats, this can be useful to spur development of the project (i.e. for people who don't want a permanent account but don't feel comfortable having their IP permanently, publicly attached to edits). Probably the reason it hasn't been done in the past is it's almost certainly going to make it easier for bad actors to fly under the radar. Before, you either had to show your IP address (which can reveal your location and will usually uniquely identify who edited something for at least a little bit; you also can't use a VPN without special permission) or you had to register a single account (where if you created multiple, a sockpuppet investigation would often find out).

So there's an inherent trade-off, but I think right-wing threats of stochastic terrorism really tipped the scales.