Why would my boss say this?

I wear office clothes, trousers and blouse, as I work in the office at a store, whereas everyone else where's a t-shirt with the logo on.

We have a new starter in the office and the boss said "when we get the new starter do you want to wear t-shirts too? Or just the way you are? So you don't have to think of what to wear everyday"

He said there was nothing wrong with what I wear. But why would he suggest it?
Why would my boss say this?
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