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> The ATtiny series is over 20 years old, but it's still selling well with very healthy profit margins because of the massive ecosystem around AVR. There are better, faster and cheaper micros, but none are as well-documented or as easy to prototype with.
As you said, with the Arduino maker scene in particular, these chips are still profitable to produce because pretty much anyone with no previous concept of computer programming can use them to make an LED blink. And for simple purposes like controlling the temperatue inside a propagator, they're still the best bang for your buck.
Within the maker scene, for more ambitious projects, the standard is now more or less the ESP32, because it can do infinitely more than standard 8-bit RISC controllers. You can do anything with it from streaming MP3 music via bluetooth to designing interactive touchscreen menus or running a basic intranet web server, at least when you buy them as part of a developer's board like the ESP32-WROOM. Documentation so far isn't as good as the Attiny/Atmegas, it's still a growing ecosystem with fewer libraries than the latter, but it's still a powerful piece of kit.
I've been tinkering with a WROOM to stream music from my smartphone to my home stereo amplifier, but it's proved too difficult because so far there are no easy to understand A2DP (Advanced Audio Distribution Profile) libraries that can get the job done the way I want.