A huge percentage of products designed today are using one or many single-source components.

In 1980-1990, you did all you could to only select components with multiple sources. Today you can't, because you will not be competitive when you dismiss all single-source components.

You will miss single-source GPS modules.
Single-source USB hubs.
Single-source processors.
Single-source DC-DC controllers.
...

The reason people write their sources in C, is that a large percentage of the program can be moved from processor A to processor B, if you find out that you need to move to another processor.

It is normally more economical to move to another processor if production is ended, than it is to select a processor with multiple sources - especially since the multiple sources can come to the same conclusion and stop producing a chip.

In a compoetititve world, you often have to redesign the hardware every 18 to 36 months just to be able to either produce something with same specifications but all the time lower production costs. Or something you will sell for the same price, but all the time with more functionality.

It's only for small-scale production where the development cost is so high that you can't afford reengieneering. But then you can normally also afford to stock up on components to handle a couple of years of production needs. You would probably even produce the devices for several years needs.

I really don't think many companies sees a problem with the AVR chips being single-source.