Here’s an example: The image below is the battleship Yamato of the Imperial Japanese Navy. She and her sister ship were the biggest, best-armored, and most powerfully-gunned battleships ever built by any nation, hands down.
Ultimately, neither of the Yamatos saw any major combat against other battleships. However, both of them ultimately faced air groups from US aircraft carriers… and they lost. Airplanes launched from carriers could strike from hundreds of miles away, and in massed attacks, they were difficult for even the best anti-air defences to completely repel. Sure, you might shoot down a few, but a dozen or so aircraft lost to eliminate a battleship with a 1000+ strong crew stacks up pretty favorably attrition-wise. Post WWII, you also saw the introduction of guided ship-to-ship missiles. Battleships weren’t completely useless (the US Iowa-class ships were in on-and-off again service into the 1990’s), but resource-wise, you can get almost a complete aircraft carrier OR multiple destroyers or frigates carrying precision-guided missiles for the operating budget of one battleship. So basically, you just get more “bang for your buck” for other types of warships in the modern naval battlespace. Navies were beginning to realize this even before WWII was over. The United States cancelled the Montana-class battleship program in favor of more carriers, and in Japan, an unfinished third Yamato-class battleship was instead completed as an aircraft carrier.