The only thing I can think of is that they think it will make them more attractive as a business. When in reality, no one picks a business on the basis of the rainbow posters in the window.
My feeling is that they didn't think it would harm, and it's cheap, so why not.
And the dedicated EDI person did all the running, the admin, the liaison. And dealt with all the training, etc. justifying their position.
But now the compliance has spiralled out of all control, and is looking like ideological batshittery, which is clearly highly controversial politically.
But, as was planned in the beginning, the masterstroke of tying transgender issues to LGB issues makes extrication more tricky.