Why do people say "Don't use place()"?

I'm not sure what evidence you have that says everyone says not to use place. I suspect if you're judging by stackoverflow posts, you're mostly reading my opinion a hundred times rather than a hundred different opinions.

I recommend against place mainly because it requires more work to make a UI that is responsive to changes in fonts, resolutions, and window sizes. While it's possible to write a GUI that uses place and is responsive to those things, it requires a lot of work to get right.

One advantage that both pack and grid have over place is that they allow tkinter to properly configure the size of the root and Toplevel windows. With place you must hard-code a size. Tkinter is remarkably good at making windows to be the exact right size without you having to decide on explicit sizes.

In addition, long term maintenance of applications that use place is difficult. If you want to add a new widget, you will almost certainly have to adjust every other widget. With grid and pack it's much easier to add and remove widgets without having to change the layout of all of the other widgets. If I've learned anything over years of using tk and tkinter is that my widget layout changes a lot during development.

place is mostly useful for edge cases. For example, if you want to center a single widget inside another widget, place is fantastic. Also, if you want to place a widget such that it is independent of other widgets, place is great for that too.

There's nothing really wrong with .place, although using grid and pack give you more maintainable code. If you want to add a feature then place would require you to alter loads of absolute placements to fit a button in, for example.

If you need to use it then use it, there's no real problem with it, it just isn't the most maintainable solution to many problems. As you say, it's a matter of preference and ease of use.

Edit: there's an excellent answer you can read about it here.