Just a question about Kroger's multiple and future goals

I worked at Kroger when I was in high-school and it was one of the first stocks I purchased.

I've never sold and now consider it a good defensive stock to moderate risk in my portfolio. It's a position I regularly contribute to.

My questions are:

1. Why do Costco and Walmart trade at such a higher premium than Kroger?

1. Is Kroger able to replicate what Costco and Walmart are doing to get such a high premium on stock price and how feasible is it they could execute on that? Can't they just merge with a clothing and electronics retailer and be more like Walmart?

Thanks