If you wanted to 'stab' some1 with something... it dosn't matter the size... hell you could go ahead and stab something with a ball-point pen......
Knives are made for utility today... not even our soldiers are getting into hand-to-hand combat with the enemy anymore... this isn't back like trench warfare... now we can shoot at the enemy from 150+ yards away...
In the military, anyone who's done a few tours will have a multi-tool on them.. and at the very most a 4-5 inch folding knife for Utility tasks... any1 who knows anything about reality dosn't have a 12 inch fixed blade strapped to thier thigh..
Personally, I don't like tanto blades... to me.. they suck... flat out... maybe it's the way im using them.. maybe its the task I was using them for... But i find the a FFG leaf-blade is the best when it comes to slicing capabilites..
Tantos... not so much..
As for a reason for a small blade with a tanto shape... eh... a "cool" factor... "TACTICOOL" seems to be selling nowadays... unfortunatly the knife makers are turning to this type of crap to make money... instead of sticking to their roots and making usable knifes ...that are realistically marketed... (instead of beating on a knife till the cows come home in their videos)... its just sad... but hey... thats why I am blessed to know some great custom-knife makers and can have mine drawn up from scratch!!!! .. screw production knives