Take it like "a couple of people" or "a group of 27 people". Who did it? The couple did it. The group of 27 did it. What kind of group of 27? of people
It is not exactly like that, but similar. The subject of the sentence is in nominative. Numbers above four and adverbs of quantity (málo, hodně...) are followed by genitive and require a singular verb. What is in nominative here is the number.
Remember, this is grammar, some rules may be strange.
just try to keep in mind that the relative simplicity of "five or more needs the genitive" gets more involved the moment the entire noun phrase with the numeral functions in a case other than the first three major ones we learn here (nominative, accusative, and genitive).
even with the noun phrase in the genitive, the easy applicability begins to fall apart for the number itself, while the counted object does remain as expected:
bez těch pěti (dvaceti sedmi) zvířat (žen, mužů, stromů).
I get the sense in which "27 animals are coming here" = "27 animals come here" would have the same meaning in English.
But when you want to translate this sentence "jde sem 27 zvířat", you are basically saying that "27 animals are just on their way here" not that "27 animals usually come here".