Or even non-pragmatic reasons we wouldn't guess in isolation. It's been thousands of years, and sometimes it's hard to track the why of how people chose to do stuff, only what they actually did.

We've lost details on how to make some of their breads because they never bothered to write it down, because why would you document how to do something everyone does regularly?

It could be something like it wasn't considered proper. Building the tomb is an honor, or something you wouldn't want to force someone to do for whatever reason.