My biggest problem is that you get excited for the first few days, then you realize that there is very little you can learn from these toy projects, and then there isn't a project that is meaningful (to yourself) enough to persue. If you look at all those motors and sensors -- you need to think hard enough to come up with a project that makes good use of them.
I browsed maybe 50 of the most viewed project on arduino website to get inspired. There are may be 1 or 2 that somewhat interest me.
Based on impression coming from secondhand marketplace listings, my very uninformed guess is that 70% of Arduino kits and raspberry pi units purchased by amateurs are sitting in their home gathering dust, including mine.
This is actually a very sad comment to read. My childhood was spent buying up every Forrest Mims circuit book I could find at my local Radio Shack, and then trying to figure out which circuits I could bring to life given a very limited amount of components I could source.
I'm not sure what it would take to make these kits more exciting, because I find them ABSOLUTELY AMAZING.
I could rattle off 100 cool projects to make with these dev kits, especially coupled with a 3d printer.
This very much depends on your initial skill level. Have you ever held a resistor? Do you know which side of the LED is the minus? How many terminals does a hobby servo have and what do they connect to? These are the sorts of questions the kits are meant to answer. You're not really learning "an arduino", you're learning a new tool to make the projects you actually want to make. To "use all the parts" isn't what I usually want out of something.
The kits themselves usually carry too wide of a selection of components to have enough of any one part for a good project anyway, but if you need more, go on Amazon and search for "<insert component> arduino" and buy them by the 10 pack.
If you decide it's not for you, then the kits were always a collection of cheap parts to begin with; not a big loss.
I have three within my range of vision if I lean a bit and look into another room, and only one gets used. And that's because I compile audio plugins to release VST2 on the Pi as a platform (compiling on a Pi 400) relying on Reaper as a host DAW.
I'm not doing audio work on the Pi, though, just supporting the platform for those (?) who do (?).
I would love to come up with cool things to do with Arduinos etc: I hacked high sample rate support into Eurorack modules that ran on Teensy, and then the Teensy that had the raw audio output pin which supported this use, hit end of life so those modules cannot be replaced now, and what I have is all I'll ever have.
The world of tiny computers is lovely but doesn't always stay accessible. For instance, I never got into hardware synth making that much, but these days all the oscillator chips etc. you'd want to hack with require robotic installation: they're too tiny for someone who grew up on DIP.
Some sort of class helps here a lot - not as much as actual tutoring, but just as motivation and audience that you can show off your projects to.
A tea-making robot you made at your home is boring. A tea-making robot you made during class which participated in end-of-class competition and got 3rd place? Much more interesting.
And if you are in CA, there is Robogames which has (or at least had in the past) categories such as "art bot" (any Arduino project which has a moving part can participate) and even "static bot" (for projects without moving parts). You get to demo your project to few hundred participants, and maybe even get a prize!
I suspect this is very subjective. I had a Radio Shack 200-in-1 kit when I was a kid and learned tons from it, working through the book and then designing my own projects.
My current project just ties in my doorbell to Home Assistant. I could have built it only using what came with my old Raspberry Pi kit. Once I finish that, I'll be tying in my garage door, another project that uses simple parts. These projects are way simpler than what I do for work (currently writing PLC code for the Navy), but they're still fun.
I browsed maybe 50 of the most viewed project on arduino website to get inspired. There are may be 1 or 2 that somewhat interest me.
Based on impression coming from secondhand marketplace listings, my very uninformed guess is that 70% of Arduino kits and raspberry pi units purchased by amateurs are sitting in their home gathering dust, including mine.