Why does quoting take so long for distributors and suppliers?

Because it's skilled, manual matching. For every request, someone has to identify each item, find it in a catalog that can run into the hundreds of thousands of SKUs, pick the right product among multiple brands and options, check stock, and apply pricing that's negotiated per customer. Kits, substitutes, and tiered pricing make it harder, and it takes an experienced person to get right — which is why a single detailed quote can eat a big chunk of someone's day.