If rigor is the whole point why are we so focused on classical math (eg classical logic) not the wider plurality?

Rigor is not the whole point of math. Understanding is. Rigor is a tool for producing understanding. For a further articulation of this point, see

https://arxiv.org/abs/math/9404236

Rigor is one solution to mutual understanding Bourbaki came up with that in turn led to making math inaccessible to most humans as it now takes regular mathematicians over 40 years to get to the bleeding edge, often surpassing their brain's capacity to come up with revolutionary insights. It's like math was forced to run on assembly language despite there were more high-level languages available and more apt for the job.

It seems you have never tried to prove anything using a proof assistant program. It will demand proofs for things like x<y && y<z => x<z and while it should have that built in for natural numbers, woe fall upon thee who defines a new data type.

In calculus the core issue is that the concept of a "function" was undefined but generally understood to be something like what we'd call today an "expression" in a programming language. So, for example, "x^2 + 1" was widely agreed to be a function, but "if x < 0 then x else 0" was controversial. What's nice about the "function as expression" idea is that generally speaking these functions are continuous, analytic [1], etc and the set of such functions is closed under differentiation and integration [2]. There's a good chance that if you took AP Calculus you basically learned this definition.

The formal definition of "function" is totally different! This is typically a big confusion in Calculus 2 or 3! Today, a function is defined as literally any input→output mapping, and the "rule" by which this mapping is defined is irrelevant. This definition is much worse for basic calculus—most mappings are not continuous or differentiable. But it has benefits for more advanced calculus; the initial application was Fourier series. And it is generally much easier to formalize because it is "canonical" in a certain sense, it doesn't depend on questions like "which exact expressions are allowed".

This is exactly what the article is complaining about. The non-rigorous intuition preferred for basic calculus and the non-rigorous intuition required for more advanced calculus are different. If you formalize, you'll end up with one rigorous definition, which necessarily will have to incorporate a lot of complexity required for advanced calculus but confusing to beginners.

Programming languages are like this too. Compare C and Python. Some things must be written in C, but most things can be more easily written in Python. If the whole development must be one language, the more basic code will suffer. In programming we fix this by developing software as assemblages of different programs written in different languages, but mechanisms for this kind of modularity in formal systems are still under-studied and, today, come with significant untrusted pieces or annoying boilerplate, so this solution isn't yet available.

[1] Later it was discovered that in fact this set isn't analytic, but that wasn't known for a long time.

[2] I am being imprecise; integrating and solving various differential equations often yields functions that are nice but aren't defined by combinations of named functions. The solution at the time was to name these new discovered functions.

The thing is if something is proved by checking million different cases automatically, it makes it hard to factor in learning for other proofs.

There are still many major oversimplifications in the core of math, making it weirdly corresponding with the real world. For example, if you want to model human reasoning you need to step away from binary logic that uses "weird" material implication that is a neat shortcut for math to allow its formalization but doesn't map well to reasoning. Then you might find out that e.g. medicine uses counterfactuals instead of material implication. Logics that tried to make implication more "reasonable" like relevance logic are too weak to allow formalization of math. So you either decide to treat material implication as correct (getting incompleteness theorem in the end), making you sound autistic among other humans, or you can't really do rigorous math.

Let’s not forget that mathematics is a social construct as much as (and perhaps more than) a true science. It’s about techniques, stories, relationships between ideas, and ultimately, it’s a social endeavor that involves curiosity satisfaction for (somewhat pedantic) people. If we automate ‘all’ of mathematics, then we’ve removed the people from it.

There are things that need to be done by humans to make it meaningful and worthwhile. I’m not saying that automation won’t make us more able to satisfy our intellectual curiosity, but we can’t offload everything and have something of value that we could rightly call ‘mathematics’.

But in this future, why will “the most compelling motivations, the clearest explanations, and the most useful maps between intuitions, theorems, and applications” be necessary? Catering to hobbyists?