Because the writers say so.
Not in their writing, no. Nowhere in ST:ID does anybody suggest that Nero even existed
, let alone had an influence on Starfleet thinking.
Certainly there's no suggestion that Nero's antics would have had any effect before
he destroyed Vulcan - say, making Starfleet build a bigger and badder Enterprise
. (And the Vengeance
doesn't appear to be all that much newer.)
They even went so far as to have the front for the Section 31 base beneath London called the "Kelvin Memorial Archive".
Quite so. And the idea was that this should look like the least significant thing on planet Earth, to hide its crucial true significance. So a name referring to an irrelevant incident would fit right in.
It's all intended to be Butterfly Effect repurcussions of Nero's arrival in 2233.
It's not indicated
to be that.
It happened a lot in TOS, but this is a pre-TOS AU
So Nero made all other space monsters disappear?
And while the DDM was something Starfleet might not encounter until sending ships to extreme deep space exploration missions (but in TOS, it had already sent two
ships to that particular spot, and one of them made a revisit!), it was apparently headed towards shallower space; the Space Amoeba was found in shallow space, as was NOMAD.
Perhaps the refit into an "almost totally new" and more powerful Enterprise in TMP? Or development of the USS Excelsior?
That's a giant perhaps, especially considering that neither of these appeared to give Starfleet any real improvement in anti-Amoeba or anti-DDM capabilities...
Starfleet getting bigger and better ships is most probably a natural development that doesn't especially benefit from individual incidents.