Why can't we just do a simple cache interface?

psr-cache.php

<?php

namespace Psr\Cache
{
    interface CacheInterface
    {
        public function get($key, &$isHit); #: mixed
        // Note: $isHit is populated with `true` on hit or `false` on miss. This
        // is a simple way to distinguish between falsey values and cache misses.
        public function has($key); #: bool
        public function save($key, $value, $ttl = null); #: bool
        public function delete($key); #: bool
    }

    // This additional interface could be for batching gets/saves, etc.
    interface MultiValueCacheInterface
    {
        public function getMultiple(array $keys); #: array
        public function saveMultiple(array $values, $ttl = null); #: bool
        public function deleteMultiple(array $keys); #: bool
        public function clear(); #: bool
    }
}