I think the world is changing, and it's often cheaper to buy the component pieces of things these days, than to buy a complete package.
If you're dealing with a product or service that takes a few radically different types of skills or inputs to build, it's unlikely that a given company is equally good, equally skilled, or equally cost effective at delivering each of those components.
And most importantly, it's unlikely that the person or company equally likes doing each part of the process.
In olden days, coordination and communication were unreliable and expensive to the point that it didn't make sense to bring multiple people in. But these days, you can often get things much more effectively by getting the relevant expert or skilled craftsman that is both great at what they do, and passionately enjoys that aspect of the process.
This is probably especially true with services. While it's nice to be able to hand over something to just one person and forget it, that usually either requires higher expense or lower quality than if you were able to assemble the component parts yourself. If it's a one-off and not-so-important transaction, that's fine and take the convenience. If it's a repeatable part of your life or business, think of going piecemail and assembling (or even getting a great assembler to make sure it works well together).