Time and Space
The running time on Eleanor Rigby is 2:06 but it seems longer.
There is no expectation inherent in classical music that sections should be of specific lengths. Pop music in some respects is merely a spin-off of technology (radio and constraints inherent is the media), and later on music videos (and film), then cut/paste sampling and remix.)
Duration is a labile phenomenon, dependent on the musical density. Classical music seems longer, probably borne of a logical sequence of shorter ideas or vignettes involving a wider range musical and timbral elements.
Here is the song, with just the string arrangement. It has a strict pulse, yet unlike pop music, even though it gets its clock from it.
The main distinction between an orchestral vignette and a pop song is that classical music spins out in the context of a larger framework. The concept album of the 60s and 70s was really a modern variation on the sonata form, or a Musical. Shorter sections joined together naturally have a coherent logic, as in literature.
Eleanor Rigby is actually a short piece for string octet, where there is a vocal part, an interesting switch of perspective. It is not really a pop song that features a string arrangement. The piece could exist on its own without the vocal parts, and is unmoored from the expectation that the grooves should fill in the side of a 45.
Given its history--from a ditty by Paul McCartney, re-shaped through various other group input, then dressed in a Bernard Herrmann-inspired scoring (apparently from Truffaut's Fahrenheit 451), the final piece is a congeries of cinematic and spatial aspects, on top of French New Wave. (In a sense Eleanor Rigby comes from Truffaut, via George Martin.)