Joseph Smith had an answer for everything. He took being a “prophet, seer and revelator” very serious. What good is a prophet if he can’t prophesize?

Find some bones in a field? “an officer who fell in battle, in the last destruction among the Lamanites, and his name was Zelph ” (Heber C. Kimball Journal). You can even buy a book on it

Find a pile of rocks in a field? “There is the place where Adam offered up sacrifice after he was cast out of the garden.” [1]

His older brother Alvin dies before he can be baptized? Receives revelation on baptism for the dead.

Lets contrast this to our current Prophets. Asked about transgender individuals, Then Elder Oaks said

This question concerns transgender, and I think we need to acknowledge that while we have been acquainted with lesbians and homosexuals for some time, being acquainted with the unique problems of a transgender situation is something we have not had so much experience with, and we have some unfinished business in teaching on that.

Dallin H Oaks press conference, Jan. 27, 2015. 

The Prophets do not know why the priesthood was withheld from those of black ancestry.

Our current Prophets don’t know about sealings of multiple wives in the next life

That same principle applies to unanswered questions about sealings in the next life or desired readjustments because of events or transgressions in mortality. There is so much we do not know that our only sure reliance is to trust in the Lord and His love for His children.

Oaks Oct 2019 Conf Address

I can’t find one instance of Joseph Smith saying “I don’t know” to some theological question, or if he did say it, he probably followed it up with a “let me ask God and I’ll get back to you”. And the next day there was a new section to the D&C!

Why do you think this is so? How come the early prophets had specific answers, and our current prophets have a lot of “trust in the Lord” answers to difficult questions?

[1] Heber C. Kimball, as quoted in Otten & Caldwell, Sacred Truths of the Doctrine & Covenants, v. 2, pp. 278-279; also in The Life of Heber C. Kimball, pp. 209-210