turrets are more squishy than inhibitors

just had a game as velkoz and at a point my team was fighting at drag and they were on a run after losing the support, and it gave me free time mid to hit the mid inhib turret. i had around 100 ad(took ad reds cuz i suck at getting cs) and i was able to finish the entire tower with only 1 canon minion wave, without second drag buff too. it was surprisingly easy. and then i found that the inhibitor was instead much harder tokill it took me less than 10 autos to kill the tower but the 5 autos i landed on the.inhib only took less than 1/5 of its hp away. this makes me feel very weird, isnt the inhib tower suppose to defend the.inhib? why the heck is the inhib tankier than the turret?