I encountered this problem several times but never managed to understand why. For example, I want to get the maximal value of a parametrized function $\log(c)+ b\log(k-c)$ with respect to $c$. I tried the following code:
In := MaxValue[Log[c] + b Log[k - c], c]
But instead of a funtion of $b$ and $k$, the output is
Out := MaxValue[Log[c] + b Log[k - c], c]
Can you explain why this could happen in this case, and more broadly, likely causes of this problem in other cases?