These teams know the failure rate of picking a QB high. What fans (still) underestimate is the value of a QB. You aren't winning a Superbowl without one in this era. No stat better illustrates that than this one -- 13 of the last 14 QBs representing the AFC in the big game were named Manning, Brady, or Roethlisberger. Coaches and GM's know their jobs are on the line without one. Owners know that the $160M+ player payroll they are funding isn't ultimately going anywhere. Your ceiling becomes "playoff pretender," and you have to sell that to the fans every year. The "anything can happen in the playoffs" mantra is nothing more than "all you need is a dollar and a dream" nonsense, and I think most fans realize that.
If there's a guy there in the top 10 that has a ~25% chance of becoming your guy under center for the next decade, you pull the trigger.