There's a difference between established industrial designs where there is an argument for maintaining compatibility and an existing codebase, and hobbyists which can quite happily move up the chain and are always looking for cool new stuff in other respects. Even in product development, some companies go out of their way to use ridiculously outdated, expensive chips. That usually only flies when it's for non-consumer applications where they can afford to throw more money at a chip vendor to keep making outdated chips at outdated prices (which sometimes even rise); for consumer products the competition will undercut you by using newer, cheaper chips if you don't. For hobbyists, it actually pays off to upgrade - you get better toolchains (no need to deal with all the ROM/RAM/pointer type shenanigans of AVRs on ARM), better debuggability, etc. Of course, it doesn't mean you should jump onto any random chip - the toolchains and ecosystems vary wildly in quality - but it's a shame that so many people just stick with the old instead of trying something new.
There's nothing wrong with the Tiny series - little 6- and 8-pin chips are still the market where AVR/PIC make perfect sense, and I'll be the first to admit that I've used a PIC12F629 as a dual frequency generator in a project. But as a flexible platform for hobbyists, I'd much rather have a Cortex-M3 over an ATmega. Back when I was using PICs more often, my approach was to, every few years, re-evaluate my personal selection of PICs. I'd go through Microchip's (extensive) part database, look at the prices, and see if anything caught my eye, then order some samples. My 8-pin of choice used to be 12F508, then 12F629. For 18-pin I went from 16F84 to 16F88. 28-pin, 16F876 to 18F2520 and 18F2550 for USB. 40-pin, 16F877 to 18F4520 to 18F4550 for USB. I tried dsPIC at one point but didn't like it; by then ARM was picking up steam and it didn't make any sense. I haven't really looked at their line-up in a while, since I've mostly moved on to other chips for interesting stuff and stick to my old PICs for small quick/dirty hacks since I have a bunch in my drawers to get rid of, but you get the idea. It never made any sense to me to get stuck with one particular obsolete part or range.