Dungeons and Dragons

Here's an alternative take based on how I've played a druid in a multi-year campaign:

The druid can pick whatever animals they'd like, but:

1. Each animal type can only be chosen once.
2. The chosen animal should be thematically appropriate for the environment (e.g. don't choose elk in a desert or snakes in the arctic).

My DM let me choose whatever animals I wanted except for dinosaurs. I didn't want to abuse that by spamming 8 wolves every encounter so I came up with these self-imposed restrictions to try to make things interesting. I think that the "each animal can only be used once" limitation in particular was very interesting because it gave the spell longer term strategic implications as well -- "is this encounter scary enough that I want to burn one of my stronger summon options".

My flavor for the restriction was that, since the animals are actually fey spirits, they didn't like being "taken for granted" and always summoned in the same form. They would only respond in the way you ask if your need was truly great