eBut when they designed the Intrepid class, who would have thought one would have ended up lost 75 thousand light years away from a starbase where it couldn't get replacements? Even if they did fail, the Intrepid class would still be in hailing range of another starship or base for back-up parts if it remains within Alpha or Beta Quads. Nobody could have foreseen a fluke accident would take the ship outside contact range thus creating an unforeseen issue.Does your computer have backups?
If it fails in the field, can you manufacture replacement microchips?
When your computer faces its nemesis, the electromagnetic pulse, do you curse the engineers for creating such a completely useless technology that should never have been installed in place of the good old abacus?
It's quite difficult to see the gel packs as in any way inferior to any other piece of technology in the real world or in Star Trek. They work fine until they fail, just like any technology. And no doubt they are extremely robustly backed up, only with more of the same, as it doesn't seem as if any other options would exist (save for the above mentioned abacus, or technologies comparable to it, such as semiconductor microchips or isolinear chips).
Except the computer I use is for my personal use, its not designed to fly a space ship. If my computer breaks, its merely inconvenient, not a matter of life and death. It seems like they can easily replace isolinear chips, but with the gel packs, they seem irreplaceable, which is a serious design flaw.
Given you're an organization who's primary purpose is exploration, with all the funky crap we've seen on TOS and TNG, including getting flung to opposite ends of the galaxy already, you'd assume it's entirely possible they could get out of range/contact for an extended period of time.
To an organization that habitually employs "secondary backups" it would be prudent to keep plenty of spares around and top off the reserves every time they stop in at a starbase. It's not like these things are taking up a lot of space that could be used for something else.