You can select any format you like. Then, if you put in 01/01, excel ignores your format choice, displays Jan-01 and puts 46000 in the actual cell. If you re-select the text format, you get "46000". The 01/01 you actually entered is gone forever.

Now imagine you load a file with 1000s of values in the form AB/CD, many are trashed. If you save the file, you've lost the original data.

All because it might save some data entry drone 5 seconds to expressly make something a date.

There are then also issues about whether "01/02", assuming it actually is a date, should be the second of Jan (US) or the first of Feb (EU, UK, North America ex US, Africa and Pacific regions). In many places, based on some arbitrary and we'll hidden settings, you will get the wrong result.

I honestly think the only reason excel does this is to force you to use excel formats and make it harder to work with non-MS products...