From Praying Medic:

There is a legal maxim that says: Never ask a question you don’t know the answer to. 

And a second: Only put a witness on the stand when you know with certainty what they will testify to.

The goal of the Jan 6th committee was to pretend they were doing an investigation while creating a false narrative about January 6th. 

The one person who knows what happened regarding the electoral vote is Pence. If the committee subpoenaed him, they would learn the truth, and it’s possible his testimony would be leaked and then the world would know the truth. 

But the committee doesn’t know with certainty what Pence would say. If they had him testify, he could destroy their narrative, or he might confirm it. Having him testify presents a significant risk.

There’s no need for them to risk having him testify when they already created the narrative they wanted. 

The fact that the committee did not subpoena him doesn’t prove anything about what happened on January 6th nor does it imply anything [about] Pence’s motives.