Think about it. The Galactic Empire builds a monstrous armored space station that's 100 miles in diameter and capable of destroying an entire planet with one huge burst from its main weapon, yet the designers left a fatal weakness in the design that not only left the most powerful weapon in that entire galaxy vulnerable but led directly to the main reactor? No shielding or protective plating in between to keep something from reaching the core? Just a long, long shaft straight to the one part of the station that would trigger a colossal explosion and make the whole weapon utterly pointless?
Then the Empire builds another one with the exact same weakness
Yep. I mean, it was different to the extent that there was no more shaft to shoot proton torpedoes into, but there were gaping holes in the second station's incomplete infrastructure that would allow any Rebel ship lucky enough to make it to the central reactor chamber to set off a chain reaction and destroy the entire thing, and if you ask me that's a hell of a lot easier than hoping your aim at a two-meter exhaust port is good enough.
Once the shield generator on Endor was knocked out the second Death Star was doomed. Emperor Palpatine grew too cocky or too stupid (or both) with age if you ask me.