Most jobs that are a step back aren't a stepping stone to a higher position (or at least, the company won't be as clear about it as yours was), so taking a step back is often something you do because you have to.

Speaking of have to, most of us have jobs primarily because we have to to put food on the table and a roof over our heads and hopefully provide for ourselves in retirement and/or give children a leg up. To the extent that we also make an impact, that's nice. But if taking a backward step tanks lifetime earnings, it interferes with the real reason we work. Let's not kid ourselves.