A very huge system library with functions for trivial, easy to derive features is more difficult to remember. The code using them may easily be less readable. Imagine you see:
a = haversine(b) Some will know, but for many, Google will be they friend, losing the productive time on that. And when the developer will need to write it next time, one may get in doubt, maybe it was hav or hsin or haversed_sine instead and need to google again. Maybe again. The only benefit, this would boost the page rank of web resources focused on this uncommon function. At the same time,
a = (1 - cos(b) )/2 (the same) would be understood by any developer in a fraction of second. haversine actually reduces readability, unless needed very often.
P.S: As correctly pointed in the comment to this answer, some rarely used functions make sense if there are code readers that have the fundamental knowledge about them, bringing up lots of useful associations. Maybe haversine is actually not a so good example if used for the task where it is commonly used (not if the expression matched just by chance). In any case the answer argues that smaller API is easier to remember and used without excessive and repeated googling.
P.S: Some "easy" functions may be present in the library if the naive formula may give overflow on intermediate result (like hypot(x, y) = sqrt(x*x + y*y)) or significant rounding errors. The actual way of computing in this case is actually different from naive.
It is important to keep the balance.