Correct. When explaining it to students, I have used the metaphor of a housing developer building homes in a subdivision: going to the OS to "allocate" virtual

Correct. When explaining it to students, I have used the metaphor of a housing developer building homes in a subdivision: going to the OS to "allocate" virtual memory is like getting a building permit from the government for a large swath of land. Having permission to build is not the same as a house actually being on that land (which is analogous to physical memory). Much as housing developers are incentivized to get permits for a large block of land at a time, general purpose memory allocators are incentivized to ask the OS for permission to use large blocks of virtual memory at a time. Asking the OS for virtual memory is very slow, so to avoid doing it a lot, general purpose memory allocators ask for big chunks and manage those chunks themselves.