I can give you the technical explanation, but why is a bit less exact.

The structure build rate increase doesn't impact starbases because they aren't a planet module, which is what the entity modifier is for.  There were no starbases when it was made, and it wasn't modified to account for them when they were added.

The missile turrets are.  The damage per second listing, without them, shows less than after you gain the research.  The reason they aren't listed on the card like the rest of the assets, is they aren't one.

The technology screens are generated, they pull the frigates, structures, and fighters from the places they're listed, check their weapons, and generate those assets for the upgrade listing.  An ability spawned turret isn't one of them and would make the process massively more complex.

I believe (though I may be mistaken) that adding them under the "frigateInfo" section in the player entity file would resolve this....they would of course have to go under the "NotOnPage" section, and would be similar to the Vasari nanite units in that regard...

This is more a balance question than a mechanical one, and therefore "a star base is a structure" is really irrelevant...that being said, there are several things in this game that affect structures but not SBs, so this is hardly the only distinction nor is it the most significant...

I would make the case that the TEC actually have the strongest line of capital ships, and are in the least need of a buff in that area...furthermore, this would create a significant synergy with Vasari SB rushes, and since there are very few (if any) interfaction synergies of this significance, I would be against this change for that reason alone....

Admittedly the Sova is rather lackluster in the current meta, but I don't think giving it a buff that almost singularly benefits a would-be Vasari ally is the best way to go about it...