It's in the idea of 'reductionism'. A kind of principle that says that we should look to explain the physical world in terms of more simple and fundamental parts. The reason this idea seem attractive to physicists, I think, is a combination of how 'successful' it's been in the past (however you want to define success in the sciences) and how intuitive it is.
It's been successful in that, ever since Newton, we have moved on to try and explain more complex systems such as gasses and the dynamics of energy (thermodynamics) and those physicists who were able to develop the most predictively viable theories were those who considered the system as the sum of some smaller constituent parts. The first of its kind was probably kinetic theory. It just worked. We were able to explain behaviour on a macroscopic scale as the sum of smaller parts which, later down the line, we were then able to undeniably detect through the invention of more powerful cameras since, previously, we could only judge the existence of these objects through the power of their ability to predict what would happen in gas systems and things like that. And science is really in the business of aiming to explain things about the natural world in terms of models that are helpful for this purpose. Perhaps the hardest phenomena to understand in terms of the sum of some smaller parts today is consciousness but some scientists argue that it emerges in just the same way that other very complex phenomena do. It's just so complex that we can't really understand it yet.
Ever since we have moved on to the much more (extremely more) successful enterprise of quantum and particle physics since Einstein aimed to describe the macroscopic behaviour of 'brownian motion' (the random motion of pollen in water) and the 'photoelectric effect' (how electrons would be emitted from the surface of a metal plate when light is shining on it) in terms of the atoms of water and 'photons' of light. Also how the Rutherford experiment was able to explain the macroscopic behaviour of materials by positing that the atoms within these materials had a certain structure where physicists thought that atoms were more like 'hard balls'. I.e. indivisible hard balls which simply exist and undergo 'hard ball' interaction. Which just means that they bounce off of one another and transfer energy/momentum to one another without loss of energy due to deformation. It's a good approximation of what we now thing actually happens. Imagine atoms like billiard balls. That's usually the analogy which is used.
Also, I say it's intuitive because ever since ancient Greece we have had 'atomists'. Philosophers that posited some most fundamental building block of nature which could explain everything. It's intuitive because it's simple. And because in life generally, perhaps we have an affinity to studying the parts of something to understand its whole.
You can find this idea online that reductionism is completely opposed to emergentism. They're not completely dissimilar. Sean Carroll (read his books they're very good) likes to discuss how 'higher level' and more complex phenomena can emerge in a non-obvious way from smaller parts. I.e. how atoms emerge from fundamental particles, how cells emerge from atoms, how orgaisms emerge from cells, how intelligence emerges from organisms, how communities emerge from intelligence etc... Ockham's razor is a powerful thing.
Edit: Oh also, I forgot to mention. Trying to understand systems that are very complex at large scales (the opposite to a reductionist method) becomes difficult because of the practicality of computation. I.e. what do you compute and how. Massive approximations are made in order to receive a model that looks anything like the complex at large and makes our understanding much less specific and more general.
Perhaps it's more intuitive to understand how one of the most fundamental parts works in its own and in the presence of other fundamental parts and then extrapolate outwards to have the most detailed understanding possible.
Like I said, science is in the business of creating theoretical frameworks that explain things. Describing a complex whole is useful but I'm not sure how you could consider it explanatory. For something to be explanatory, it seems like to have to extrapolate to new knowledge. In most cases, knowledge of something you can't see because it's so small.
I direct you here for more information:
This is Sean Carroll's blog and there are many more articles on here about the debate between reductionism and anti-reductionism.