Seeing speedruns that require such precise execution and the utilisation if glitches that require a deep understanding of the inner workings of a game just makes me feel so dumb. My question is how are they developed.

Everything take time so About make u feel dumb isnt true at all. it Depend what game did u like or Get use to it

Ok Let me Example to u Like this...

Mario or Games Runner that use something like u said that made u feel dumb. They Cant run every games to get WR (they are good of what they are)

Like I Dare WR Mario Runners to Run Dokapon The World or Some Other Games like that to Get WR (They Cant so They Dumb Right? No!)

Dont Compare Everythings and Make U feel Dumb - People Good For What they Are Train for

All that is required is a lot of time and dedication.

Lots of time with the game, an active community, and a good deal of luck.