You would be surprised about the time and skills it takes... let's just say that I use a tool meant to teach kids lmao https://www.tinkercad.com/
It's not hard, really. I grab my caliper, take measurements of the diameter of the analog stick, write them down, open Tinkercad and it's really just a bunch of cylinders I'm working with. Often the hardest part is finding a good logo that will print.
The real time wasting stuff is when I make them too thin and feel too flimsy, or when I print a test one and it's either way too loose or not large enough to fit.
Now that you know how modest the skill set to design those specific things is, on to the other issue, money: a 3d printer isn't a trivial impulse buy, but basic ones can be bought for around 200 euro! For example my Xbox analog cap has been printed on a (now discontinued) Monoprice Mini Select v2. 160 euro when I got it. There's sub 100 ones but I don't know how usable they are, plus they're even smaller and size does make a difference in what you can print.
Switch Pro lacks analog triggers and depending on what games you play it can be a really bad thing.