Why in physics does one ask increasingly fundamental questions of matter?

Question

Many physicists seek to understand grand theories of everything by reduction to smaller components or building blocks. Those trained, but maybe are not practicing talk about the importance of "first principles," (e.g Musk). For the professional physicist who might have more experience in this regard, what is the practical benefit in explanatory value of studying something (like fluid dynamics) at increasingly more basic/marginal levels?

I apologize if this question sounds simplistic, but what motivated me to ask this it is to understand it in relation to the other sciences.

I understand, one could simply quip "imagine asking that question 100 years ago, and that'll answer your question." But that doesn't really get at the "why" it's practical; it only is the result.

EDIT: Sabine Hossenfelder, theoretical physicist even has a bestselling book that argues against finding extremely elegant solutions for theories of everything.

Answer 1

Regarding

one could simply quip "imagine asking that question 100 years ago..."

That ain't a quip...

In 1841 ($\pm$a year or two) a London exposition exhibited the many clever, but not very practically useful, little electrical devices that had been conjured up following Ampere's 1820's discovery of the relation between magnetic and (changing) electric fields.

Among the attendees was Michael Faraday, also one of the founding fathers of the theory of electricity and magnetism. And, as it happened, another curious attendee was Queen Victoria. She eventually found her way to Faraday, and after some polite discussion asked...

Queen Victoria:   Professor Faraday, of what use are all these electrical gadgets?
    (and after a short pause)
Farady:   Madam, of what use is a baby?

Several years later, the first telegraphs were deployed, followed a few decades later by the transatlantic cable, and a few decades later by radio.

As for the

"why" it's practical

these fundamental theories are "tools" that engineers have at their disposal to conjure up cleverer and cleverer devices. And a more fundamental theory is a more universal tool, from which a wider variety of devices can be conjured up and constructed. That's no guarantee that any of these devices will actually be useful, but it hasn't failed yet. Indeed, it's succeeded beyond anybody's wildest imagination (even the Queen's, and probably even Faraday's).

Answer 2

The practical part of your question is answered nicely by John Forkosh. There is no way we could at present guess at the practical applications of a theory of everything, but previous experience more or less projects that there will be, inevitably.

I will address this:

benefit in explanatory value of studying something (like fluid dynamics) at increasingly more basic/marginal levels?

similar to what Faraday said to queen Victoria:

what is the benefit of a painting by el Greco, or any of the masters?

what is the benefit of James Joyce's literature?

etc., wanting to point out that human nature contains creativity. Once a physicist has the mathematical tools, in addition to logic, creativity takes over for the few gifted ones, and it is as inevitable that they will use the tools to express their physics intuitions, as it was that el Greco would paint. Very few reach that level, similar to there are millions of painters but few that really are acknowledged as masters. The rest of us physicists, are lucky that they appear, as Feynman did and gave a great push forward in calculations.

Creativity is driven by intuition and a sense of beauty, and "rightness", and the more involved theories of physics are beautiful, for those that can understand the mathematics, even though not art, simplicity being a driving force. That is why the theory of everything is attractive as a goal, and all unification theories.

Now for

of studying something (like fluid dynamics) at increasingly more basic/marginal levels?

Physical theories have many mathematical frameworks, and it is satisfactory to be able to prove that at the interface there is complete understanding. Understanding is another human trait, and one wants to know how the various frameworks fit the same observations. In chasing for this goal, new effects can be found, look at transistors and other quantum mechanical applications, once quantum mechanics was understood.