Even with a fair bit of general lichenological experience, a person can wander a diverse, old forest for hours encountering a tremedous variety of lichens yet come acoss few, if any, calicioids.  Meanwhile a person who has developed the "eye" for where to look might have found a dozen or two calicioids. The simplest reason for this is that calicioids tend to grow where there are few other lichens.

Most seem to be slow growing and avoid competitiion with faster growing lichens by growing in areas that are sheltered from liquid water. These are the best knon calicioids, and the most commonly collected. They are strongly associated with old-growth or "legacy" forest conditions. This is partly because only large (old) trees are able to regularly form zones on their trunks that are sheltered from rain. That said, it does seem that bark and wood must be sufficiently aged to become colonized by calicioids; I have seen younger trees develop sheltered dry areas without becoming inhbited by calicioids.

A second group gets ahead of the competition by growing on rather young branches that have simply not yet been heavily colonized by other lichens. These speedy calicioids probably do grow faster than calicioids in dry habitats, but they also are tiny, so they just don't require a lot of growing before they start producing spores.