Why is sunflower and 20/20 so hard to find on vinyl?

Im trying to increase my beach boys collection and i was curious to know why some of them are so rare for the most part. Wild honey and friends can be pricy but i tend to see them always available on ebay and discogs and pet sounds and everything before are pretty easy to get. The same cannot be said for sunflower and 20/20. Sunflower i haven’t been able to find at all and I’ve only found a couple copies of 20/20 for a big price. Why are these 2 so hard to find on vinyl?