Robots are often made multi-purpose.
They're usually not redesigned for every other application, that'd cost quite a lot.
A company that would like to use a robot, (let's say a packaging company) often doesn't have the knowledge (or experience) in designing and manufacturing robots.
The company that would like to use a robot, often doesn't even have the knowledge to program/implement it into their workflow.
Let's say there is a company that's selling bottles of water, called WaterB. Pretty straight forward. Since they do not design robots on a daily basis, they're unlikely to have personnel that can design and "create" a robot efficiently. It will not be cost effective to design a robot for a one-off, and it will have some "quirks" since it's the first version of a company with no experience.
The WaterB company now has a choice, hire another company to design a completely new robot, buy an existing model (and implement it themselves) or hire an "system integrator" (company).
Usually, they'll hire a system integrator, they'll go over the benefits and problems that robots may have and check if there are points in the bottling proces where robots can be used efficiently.
WaterB (or if used, the system integrator) will then most likely buy an existing model of robot, and program it to "palletize" the water bottles.
So yes, there are companies that design and manufacture robots (obviously), but it's often not really something you do "in-house". Due to the long design, development, testing and certification proces.
Designing/developing a robot usually only pays back when you're going to sell multiple of them.