We're looking at over 3 full seasons since he has taken a meaningful snap.
We're looking at the 2013 playoffs since he last did anything of any particular relevance (in which he had the Niners in the NFC title game and like 6 yards away or whatever it was from going to a 2nd straight SB.....until he tested Richard Sherman at the wrong time).
Was 2012 / 2013 Kaepernick better than Brian Hoyer at pretty much any point? Absolutely. Would it be worth taking a risk on getting no better than 2014 - 2016 Kaepernick (meaning likely at this point a team won't even get THOSE not-particularly-great versions of him, after having been out of the loop for so long) vs. a guy who has started meaningful games in the NFL in the last few years and knows the Pats' system? Likely not....and those people who keep beating that drum are delusional.