If a QB has enough time in pocket, eventually someone will get open. Pure coverage sacks are very hard as WRs have knowledge of the route and timing with QB while CBs are trying to catch up.
However, Tennessee’s issues in secondary are all over the place. It starts with no pressure in the pocket so opposing QBs are able to throe dimes and their WRs get open. Also, our LBs virtually are non existent in pass plays over the middle so there are always easy slants, short passes there. Our safeties seem out of position a lot. Not sure if that is due to them coming up to help LBs or just making bad plays.
Finally, after GA game this year, the defense changed. Their effort and passion has decimated like they gave up. After first 3-4 games, local radios were talking about how good our secondary stats were and how we had not given up long plays etc. that all changed in a hurry.
In short, it is combination of bad coaching, poor effort and lack of other aspects of defense to help them out.