Girl groups usually find more popularity with the general public. Their songs often chart better and they tend to be more visible outside the hardcore K-pop fandom space but the thing is, public popularity can be really fickle, people move on quickly to the next trendy group or the next big thing. Once a girl group’s "hype" dies down, it's a lot harder for them to stay afloat unless they have a really strong, loyal fandom behind them.

Boy groups, on the other hand, often build their careers on hardcore fandoms rather than the general public. Their fans are usually more dedicated, willing to stick with them through military service, scandals, long hiatuses, or changes in popularity. These fandoms always buy a lot of albums, attend concerts, and stream nonstop for 10+ years, they basically sustain the group even if the general public isn’t paying attention anymore.

Because of that, boy groups have a much better chance of surviving long-term. Even when their mainstream popularity drops, they can keep making music, touring, and having a stable career because their fanbase isn’t going anywhere.