It's easier to make a very specific style of application that's very similar to what a lot of other people make. Anything outside that is probably significantly more difficult though, because of the massive complexity of everything your software has to interact with.

It's a little different imo. We've settled on the design of the jet engine through math and engineering. The shape of it is designed and not arbitrary. On the other hand, the syntax of a programming language is entirely arbitrary, settled upon by whoever wrote the tool using whatever convention struck them at the time. Programming languages weren't designed and come upon through linguistical theory or psychology over what might be the best way to structure this stuff or anything like that. It wasn't rooted in empirical evidence like the jet engine is. It was a programmer at AT&T deciding that grep seemed like a pretty cool acronym 50 years ago, and we are still teaching kids how to use grep today for no reason other than this arbitrary syntax now being the status quo due to everyone in the business having already taken the time to learn it. Not because it's good or we have some evidence that this is a decent syntax, only that we are lazy and entrenched.

> the syntax of a programming language is entirely arbitrary [..] Programming languages weren't designed

This statement is quite simply wrong. Unless I'm misunderstanding you, you seem to be ignoring decades worth of programming language research and the years of work put into designing individual languages (whether by BDFLs, communities, or ANSI committees).

I agree with you that perhaps jet engines weren't the perfect metaphor. However, I think that that's because jet engines have much more stringent external (physical) constraints than software or programming languages. The latter do allow for a certain amount of "taste-judgment": it doesn't matter too much which way you do it, but some people at some times prefer one way over another.

So a more apt metaphor might be architecture: We've known how to build houses for millenia, but we're still improving our materials and techniques, while tradition and fashion continue to play a big role in what they end up looking like.

I get that programming languages are designed by committee and every decision is thought out, but that still makes some things arbitrary to whatever they decided. It really is arbitrary that a for loops is done like this in python:

for val in sequence:

  print(val)

and this in R:

for (val in sequence)

{

print(val)

}

and this in bash: for val in sequence; do echo val; done

I mean there was no paper that I can find that found curly braces to be especially drawing to the human eye or anything like that. or that it's particularly intuitive to write "do" and "done" or not. For loops look like no linguistical sentence structure that I recognize, they are pretty much their own thing structurally imo. These are all arbitrary decisions decided by people, because it just happened to make arbitrary sense at the time for any number of reasons. Not because the R core team ran some psychological experiments to empirically determine the most intuitive for loop structure when they drafted their language; that data has never been collected, the R core team just followed what the S team had already done and that's that. Arbitrary.