Had the GBA architects made the device halt on invalid memory rather than return the last thing on the bus and hope everything would be ok this entire class of bug wouldn't exist and the authors of that code likely would've found that bug during production.
Of course, would it matter if these bugs were found? The games ran fine on real hardware.
There’s no maintenance burden either, because updating a gba game is literally impossible.
Not quite. The Pokémon Ruby/Sapphire Berry Glitch bug was fixed by connecting to games that had a patch program, such as Pokémon Emerald, the 3rd in the Ruby/Sapphire/Emerald series.
Hey now, I'm sure it's not "impossible", you could probably overwrite specific sectors with laser or whatever, but probably had more to do with the distribution, where the economy and environment impact wouldn't make sense.