Typical retailers have around 20% to 40% gross margins and about 6% net margins (on average). Even grocery stores (the sector with the thinnest margins) do better than 0.5% at around 2% net margins on average.
Large retailers can easily afford to to build good technology. The problem for them is not one of financing, it's culture. Most retailers, even "luxury retailers", have a deeply engrained culture of being extremely frugal. I once worked servicing that sector and recall visiting a higher end jewelry retailer. The store area that customers can see was very posh and slick. But step into the back office and everything was dingy and run down. This sort of thing is a conscious decision on their part.
Most of these firms will NOT pay top dollar to hire the best talent even if they could afford it. Most do not understand software development even a little bit. Most do not understand the role of technology for anything other than record keeping (at best). But (usually) they're not run by idiots either. So when they recognize these issues and try to isolate the "online" retail from the rest of the firm (e.g. Walmart), it creates a substantial amount of friction and rivalry. I've seen it first hand and, sadly, there is no simple solution.