Inconsistency in object pronouns with parler and penser

Question

I'm curious about why we say "Je lui parle", but "Je pense à lui.  Can we say, "Je parle à lui" and Je lui pense"? Why does "parler" use an indirect object pronoun and "penser" use a stress pronoun? What is the reasoning behind this? Is it something to do with the meaning of the verbs, or is there no logic to it?

Accepted Answer

Belinda, 
Just the way it is for some verbs - penser being a common example. ( Some rhyme to it perhaps, but not necessarily lots of reason! )
See link on verbs that take an indirect object that cannot be replaced by an indirect object pronoun. Note also that ' y ' and ‘ en ‘ are adverbial pronouns, and not necessarily 'forbidden'.
https://www.lawlessfrench.com/grammar/indirect-objects-2/