Dedicated applications to process RAW files exist because some things are best done from RAW (like noise reduction) before conversion to an RGB format (because RAW are not RGB formats) and because there are many specialist algorithms that can be applied to RAW to reduce artifacts from demosaicing in special situations.

In particular noise is "spread out" by demosaicing from RAW formats (which all images start from even if the camera does not explicitly support RAW files). Once this is done you cannot undo the effect. So noise reduction needs (ideally) to be done as a first step in RAW development.

As you cannot undo RAW conversion to an RGB format, you cannot undo the effects of noise and artifacts in images as well as you can from RAW.

Now for most people this is unnecessary as they'll frankly manage fine with the JPEG straight from camera. But for some people who want to squeeze every last detail from an image the extra detail of dedicated RAW developer applications is worth it.

Note that something like the Camera Raw plugin in Photoshop is essentially an application that sits between Photoshop and the RAW file.

In general there is a software philosophy at work which tries to make separate units or applications to handle specific tasks. This lets developer isolate tasks and optimize them without complicating the software development process in undesirable ways.

Is it just the marketing strategy of companies to divide their software into pieces to make more profit?

Blame your camera companies.

The camera makers seem to feel that changing RAW file formats with every new model makes some kind of sense and, not only do they not make the formats public (making it very hard for software developers) but they've even been known to encrypt parts of RAW files. They could use a common format that would make software development easier for all concerned, but they don't.

As software development costs money and as the makers of software have to at least break even, it's not surprising that commercial software that reads RAW files costs more money for new versions.