If Thompson thought about that move for a while why not cut him before the start of offseason practices???
"Thought about it" and "decided upon it" are two different things.
Let's assume for the moment that the question was narrowed down to "Taylor (relatively cheap but is he adquate?) vs. Sitton (is he adequately recovered from wear and tear? and cap savings for carryover to next year). There is evidence to believe this is the case since Taylor worked at LG in preseason.
Then Sitton becomes a Goodson-like situation...there is little advantage to cutting him before they did. In fact the only advantage would have been avoiding $300,000 roster bonus dead cap hit, a small price to pay if it turned out they were not happy with Taylor as they worked through camp or if Taylor had been injured. Or perhaps they were looking to have Taylor and Tretter compete for the job which was derailed when it became evident Linsley would not be able to play. That would require a more extended look at Taylor before letting Sitton walk.
Another factor might be contract discussions with other players. It's been reported that Sitton was unhappy that he was excluded from contract extension discussions. Who with? Nobody has signed one yet. But with discussions taking place, the Packers probably have some inkling now of what these several 2017 FA O-Linemen will cost which they did not have earlier, and it's a fair assumption the numbers are not adding up.
It's been speculated by some that the Packers may have asked Sitton to take a pay cut. Perhaps, but that would likely have been asked and declined some weeks ago and would not have factored into the late decision.
I'm not happy with the move since it has been my thinking going back over a year ago that 2015/2016 was the prime window. This is compounded by the fact that I see Taylor stinking it up, very inconsistent.
I temper that with my oft-repeated formulation: winning comes down to having the roster play above the cap cost. That would have been a higher bar for Sitton than for Taylor. That will be a small consolation if Taylor keeps missing second level run blocks and shows himself to be turnstile in the passing game, an outcome which is clearly possible based on past performance.