I think of two hand openers like I do fountain pens and manual transmissions. They're less convenient but there's an intrinsic value to the inconvenience itself. The extra little effort makes you more conscious of the process and can often make using the item feel more special.
As it turns out though, I don't want that special experience with my knife when opening a package of bacon are 630am on a Tuesday. I just want the damn bacon out quickly. So, for most tasks, I'll be sticking with a one hander.
Indeed, it's called nostalgia. I would say that fountain pens are somewhat poor comparisons. I have a collection of fountain pens, and I have never in my life found a ballpoint pen that writes as smoothly as one of my fountain pens. So, I recognize the older technology as still being excellent. Knives are not that way, in my estimation. I have many modern folders which cut what I need cut easily, as easily as they are deployed. There is literally no situation I can ever recall in my life where I had a knife, cut something and thought, "Man, wish I'd had a little slipjoint, this would have been a lot easier!" I recognize that your mileage may vary.
I want things that will take some work, and for me, a traditional knife just isn't it. Small, non-locking blades that are a pain to open with gloves, and require both hands? Pass.
As for manual transmissions (all my cars have been two door coupes with RWD, big motors, and a manual) they have historically performed better than automatics. It's only recently where companies have created automatic transmissions that shift faster AND deliver better fuel economy, so delivering an all around better, more efficient experience. So, I can understand that there's a level of nostalgia involved with buying a car with a manual transmission. Now, all that said, I respect that some folks have that nostalgia about knives. However, the question being asked just kinda comes off as judgemental, as I stated in my above post. No one should presume to tell me what I need or don't need, which is what this thread is essentially doing. "Come in here and explain to me why you need a modern folder, because I don't think you do."