But in some important matters, which gave Paul difficulties getting his converts to believe in, such as:
a) future resurrections (1 Cor 15:12-22) (despite “the Lord's own words ...”!)
b) the kingdom of God is not for “flesh and blood” (1 Cor 15:50)
Paul's inability to bring about “teaching” of Jesus was probably due to Jesus and disciples (such as Peter) believing in no resurrections and in the Kingdom to come on earth.
See here for a).
then search on > 6.2 < for b).
And what about the Kingdom to come soon?
In Paul's letter,
it's a given and likely the main cause for the
conversion of the early Christians. Paul did not have to offer
“teaching” of Jesus to secure that notion. Furthermore, it was
not in the interest of Paul to say that Jesus preached that more than
twenty years earlier!
And, since I happen to think that Jesus' main message was "Blessed are you who are poor, for yours is the kingdom of God." (ref: Lk6:20 & Mt5:3) (see here then search on > 16.2 <), Paul could not preach that, for reasons I explained in my aforementioned webpage (and Paul knew Jesus was poor: see here). In a few words, middle class & wealthy people had become converted and were providing money to Paul & his helpers.
Instead Paul focused on the “high context” Christ crucified (& resurrected), invoking revelation from above, and developing all kind of theological implications with the help of the OT. Any “teaching” bits from an uneducated poor Jew to other poor rural Galileans would then be rather puny, obsolete and irrelevant relative to that new Pauline Christology (however a few of them surface in the Q source: see here).