JOIN with one very small input table takes surprisingly long

[hannahbast]

On UniProt, the following query takes over 2 seconds to join a 3,625,744,142 x 2 table with a 33 x 1 table. Shouldn't this be much faster?

PREFIX taxon: <http://purl.uniprot.org/taxonomy/>
PREFIX up: <http://purl.uniprot.org/core/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT ?protein ?organism WHERE {
  ?protein up:organism ?organism .
  ?organism rdfs:subClassOf taxon:83333 .
}