Today I was opening a #10 can of pickles with my wall-mounted Daisy can opener made in 1926.
In past decades I have used electronic openers, battery ride-arounds, P38, various plier types and
modern wall mounts patterned after the Daisy. None of these new copies last year,

Simple question. Why can't modern manufacturing techniques. metallurgy, and computerization produce a can opener as good at the 1926 model?
Surely the patent has expired. Just copy it.

It is simple, it works every time on any size can and the mount even accepts a knife sharper that also works. Swivels out of the way too.

I have a second one made in 1952 that is exactly the same design. What happened since???

Planned failure.

Cheapness. Cutting corners to increase profits.

(Pickles come in cans?)

Dazey made big wall mount, table mount, and then the little countertop electric openers.
Here's what I could cobble together as a guess for now:
About the same years as you mentioned frozen food started getting to markets. New homes got electricity and a refrigerator and a freezer.
Then the agribusiness marketed their own flashfrozen items (ho ho ho green giant) which went from their factory right to the supermarkets along the newly built interstates.
So Dazey's market is down to prepared foods like canned ravioli and soups- smaller cans and countertop sales.
And then institutional food preparers started selling complete meals ready to heat in oven or microwave.

The bean counters finally realized that the longer a product lasts, future revenue declines. Some savvy companies cope through on going product enhancements, increasing their market share, or cost reductions. Common utility products such as a can opener doesn't present many options other than cost reductions that can and often does result in a shorter life cycle with the need for more frequent replacement.

That is what you get when you demand equality.

Well, actually, in 1961 Daisy went out of business,..
because fewer and fewer folks needed a 'new' can opener.

Kinda,
kicked their own can.

Funny story about the can opener.
The tin can was around 40 years(!),
before the can opener was invented. (🙃)
Gallagher

p.s.: Their IS, however, a NEW can-opener design(!).
A 'Safety Can Opener',..kinda like this: "iheyfill safety can opener".

What's cool with them is:
1. The cut can-top has NO sharp edge.
2. You can use the cut off can-top, as a lid,
for the can(!).

They are pretty cool.

p.s.s.: "Yes we can!
...if we just had a good opener."

I believe the OP was demanding can opener quality, not can opener equality.

Yes, but I believe he is too late.