Adobe is the industry standard in graphics software. Of course, there are plenty of others but no one does it better than Adobe. All of their software is synchronized, optimized and they all do one specific thing, perfectly. One day, there may be a new collection of software from another company, but right now Adobe rules.
Why not Word or PowerPoint for a Facebook ad? Other than being ugly… exportation. Adobe software was designed with the idea that document exporting should be optimized for print or online output. If your image looks nice in Word, but as soon as you try to put it on your Facebook page it looks like a total mess, then this software is not made to export optimally.
The Adobe Suite and their functions

Photoshop: photo editing and manipulation with filters, export optimization and management of color modes and document formats

Illustrator : vector graphics software for logos, icons, book illustrations, product packaging, and billboards.

InDesign : layout and page design software for print and digital media

After-Effect : cinematic movie titles, intros, transitions, animate a logo or character

Premiere Pro : video editing software for social sharing, TV, and film

Lightroom : create, edit, organize, store, and share your photos across any device

Fresco : illustrations, drawings, optimized use of the graphics tablet

Word : documents, reports, letters, and résumés.

PowerPoint : text, diagrams with animation, images, and transitional effects, etc in the form of slides
Having the proper software is not all, you also need to know how to use them and understand graphic design. Many other software from the Adobe suite are also available for more specific needs (Audition, Bridge, Xd, etc.), but these are the main ones used in our agency. And yes, we also use Word and PowerPoint, but NEVER for our visuals!