Looking at that least, all of them except Denver made the switch when their season was already heading for the crapper. Dallas has gotten lucky that their change produced some immediate effect (or just luckily coincident with the team's general impriovements or matchups) and that Philly and New York have fallen apart.
Denver is the only team on that list making the switch while already being a serious playoff contender.
I think Dallas and Denver were in similar situations. Both have enough talent that they shouldn't be scrambling for the last playoff slot, but were underperforming on offense. Loss to division rival that puts them in third, and yank the trigger on the old QB. True about the others, they've given up on this year and are looking to the future.