The difference is perception.
1. Early use of MIM parts in firearms was less than ideal.
2. Firearms have a history of being hand-crafted by skilled artisans. Any move away from that is met with complaint even though the practice is unsustainable in today's world.
3. MIM was a move to cut costs, not improve the product. People have a negative reaction to cost cutting measures even when it benefits them.
Use of MIM in other industries doesn't suffer from these perceptions because the target market is different (or entirely ignorant of the technique) and because those who are aware understand the benefit of the practice vs other methods.
Even though I am aware of the benefits or at least the reasons for its use, I still put greater emotional and historical value in my older Smiths *because* they were carved from steel and fitted by hand (mostly). They are mechanical works of art to be appreciated for decades and handed down over the generations. My newer guns utilizing MIM are just tools to be used until they wear out and then replaced with like copies. Just like an aircraft engine or Toyota Camry transmission.
Chris