It's one of those things that isn't ALWAYS a problem, but when it is, it's pretty bad...
It kinda started with really thin, cheap motor tubes in some kits (especially Estes, but others as well). I remember building kits back in the 80's where a motor hook alone was pretty typical, especially for low power (>A, A, B, C) motors. I guess maybe the tubes were thicker or something, I dunno. Anyway, at some point it started to be more of a problem... the motor hook alone either couldn't hold up to the acceleration forces of the motor lifting the entire rocket by pushing on the motor hook front end, which would tend to rip out the side of the motor tube where it was slit to pierce the side of the tube at the upper end of the motor, therefore 1) focusing all the forces on this small spot, and 2) introducing a cut into the wall of the tube at this point, therefore weakening it, and creating a spot where the tube could tear from the ends of the cut when excessive loads were applied by the motor in flight. The other issue was that motor ejection charges got stronger (in Estes motors anyway, which accounts for most of the LPR motors flown-- the so-called "shotgun ejections") and that sudden blast could create enough pressure pulling down on the motor hook when the charge went off to "rip" the hook back down the motor tube.
Once the motor tube is torn up inside the rocket, fixing it is especially problematic. Usually the only real way to fix it is to try to rip the entire motor mount out of the rocket, centering rings and all usually, and then build a new one, and try to install it inside a body tube that has been scraped or sanded to remove as much of the old glue and mount remains as possible, without destroying the rocket in the process... Either that or just "live with it" and tape or shim the motor in place and hope it holds.
There are several "prevention strategies" that can be used... Dr. Zooch kits typically include several of them in the instructions. The old adage "an ounce of prevention is worth a pound of cure" is especially appropriate for this issue... First, since it's necessary to "slit the tube" with a hobby knife to create a penetration for the motor hook upper end to stick through the tube wall from outside to the inside just above the motor, it's recommended to "harden" the slit with a drop of ultra-thin CA glue once the motor hook is installed... this will soak into the paper tube material and "harden" it in the areas adjacent to and surrounding the hook penetration, helping to spread any loads into a broader area of the tube and strengthening the ends of the cut slit to greater resist tearing. Secondly, a strip of paper is usually glued around the motor tube immediately BELOW where the motor hook penetration cut is made, before the motor hook is installed. A roughly half-inch wide strip of printer paper or thin cardstock, with a thin, even coat of white glue applied, is wrapped around the motor tube with its upper edge just touching the bottom edge of the motor hook "slit" in the motor tube... this gives a "reinforcement band" to the tube to prevent "shotgun ejection charges" from potentially ripping the motor hook backwards in the tube when they go off. Thirdly, a "thrust block" motor block ring is usually glued into the top of the motor tube to take the acceleration forces of the motor's thrust and spread it out through the motor mount and centering rings into the rocket's airframe, rather than having all that load being taken SOLELY by the upper tab of the motor hook penetrating the wall of the motor tube, creating a focused spot of high stress.
As mentioned elsewhere, this is typical for low power rockets. HPR kits/rockets usually don't use a motor hook or block, due to the differing lengths of the casing and clearance issues with the ejection well cap and the upper end of motor hooks when installed in a rocket. Typically HPR motors have a wider ring around the bottom of the motor that acts as a motor block to transfer thrust into the airframe, and often use a rear-mounted motor retainer of various designs. Mid-power rocketry has had a lot of "overlapping" of techniques, depending on the diameter of the motor tubes and intended motor types to be used... but of course over the last decade or two we've seen a proliferation of different length motors used (more like HPR motors) so that kits built with a motor hook for a "standard" Estes D motor cannot use the one-inch longer Estes E motors without either 1) sticking out the back (which can cause stability issues by moving the CG back) or 2) removing the upper end of the motor hook, by grinding or filing it away, or 3) modifying the kit to install a longer hook for use with the longer motors when building the kit, and using a spacer ring when using the shorter D motors. Increasingly there tends to be more of a move towards rear motor retention without upper thrust blocks and motor hooks in MPR rockets anyway, and this is probably a good thing, ESPECIALLY as we see more new motors coming out departing from the "traditional" sizes of the Estes D motor and even E motors. If minimum weight is still the overriding concern, or the kit is only designed to use a specific motor (the use of a pair of Estes "D" motors in some TLP kits immediately comes to mind) where substitution or use of larger motors may make them unstable or isn't recommended, then the good old reliable motor hook and thrust block ring in the tube is STILL the best solution to the problem, with the "beef up techniques" mentioned highly recommended. Not EVERYTHING NEEDS to be capable of having different length motors installed using rear retention and thrust rings.
Later and good luck! OL JR