We know all the amino acids involved. We know how and what proteins are synthesized. We understand organic chemistry, Yet, even with all this knowledge, the basic building blocks and our modern technology we can't reproduce it. We're not starting from scratch here, it should be simple.
It's not that simple.
We don't have a clue how the whole thing works on a fundamental level, seriously we don't. There's a couple of places where knowledge is starting to gel, we learn about Glycolysis or the citric acid cycle in school, but these are more exception that rules. Just to take one example the most common experiment I'm asked to analyze are immunoprecipitation experiments. These are basically taking one protein, and attempting to see what can bind to it. We're trying to build these pathways one step at a time.
It's complicated, some things bind better than others, some things seemingly bind to everything, context is important. You have to follow up in other ways. Is this protein being seen here or there. Is it really in the cell membrane at this time? What else does it do? No one protein does one thing. If it's floating around in there odds are it's going to react with something. Pure chaos, that sack of random chemicals. We don't even understand what 90% of the DNA does on a basic level. Junk DNA my ***, that stuff we thought we threw away seems to keep doing things we don't expect. Good luck stitching all that together. Give us a few hundred years of doing this, hopefully someone makes some leap in technology that makes this knowledge come faster, but building even a basic system one block at a time is painful.