The TSA has the unfortunate and thankless job of  balancing the likelihood of people jamming an explosive up their butt with the privacy of whiney and entitled flyers, then determining how deep to scan based on that risk assessment. The failure rates will always be high because the soft spots in the security are quite apparent. 

Want to get a bomb on board? Simply shove it up your butt! Utility knife? That will fit up your butt, right next to the bomb! 

What are they supposed to do, cavity search everyone? 

Or how about gassing a plane... Do you know how much poisonous gas can be created using 3x 3-oz bottles of liquid? 

At the end of the day, the TSA can only go so far and still be within reason. If you want high success rates, the only way to accomplish it is with no carryons, no clothing, a CAT scan and a cavity search before every flight - for each passenger. So if you want to keep complaining, use one of those 3oz bottles for lube because the Feds probably won't provide it.