why is waste heat "garbage"?
Because it's low temperature and high entropy.
...that we are currently actively cooling parts and attaching heat sinks and radiators for merely decorative purposes?
No, we do it because the devices need to be cooled and it's not worth the expense of slapping a thermocouple on them for the pitiful return one would get.
and if waste heat is an actual phenomenon... why NOT harvest energy from it?
See point the first.
complexity is low with no moving parts.
We've been making ICEs for a long time; we know how to make them reliable. Just because an alternative is presented that's solid state doesn't mean we should automatically jump on it.
price is currently high but as with most things, that can come down with research.
Then report a story that says "powers car" instead of "could one day power cars"
so waste heat exists. power can be harvested.
Never in dispute, but that doesn't mean it's worth doing. Look at it this way, would you go to the trouble of putting a heat exchanger between your bathroom plughole and the inlet for your heating system? There's waste heat there too, but not enough to justify the expense you'd be in for. That's to say nothing of the fact that it would be immensely more efficient than a theromelectric doodad.
i don't see what the point of your tirade is.
I'm guessing here, but maybe it's because the parent is frustrated that you don't appear to see that there's a reason it's called waste heat. Seriously, a large sink sitting slighty above ambient temperature may hold quite a lot of energy, but it's not practical to try and extract any work from it. As an exercise, read up a little on two things: Carnot efficiency, which has been covered nicely by posts above, and low grade heat, which is only really useful for heating something colder, not anything that needs a temperature differential (i.e. any heat engine, solid state or otherwise.)