Because you can't cache things forever. Data may change out of band, and then you'll get an inconsistent response. Depending on the consistency level you are requesting with (by default

minimize_lantecy

) you'll be able to reuse caches for only 5 seconds (by default - you can change that if you want). If you want better cache usage, use zedtokens, because then you are telling SpiceDB how much staleness is acceptable