Some professionals prefer having a dedicated screen positioned in portrait mode to serve their needs better, while streamers might require dedicated screens to record their gameplay.
It depends mainly on the use case scenario of the person, but typically it is far better to have one single ultrawide for better multitasking. The 49-inch form factor with its 32:9 aspect ratio is equivalent to two 27-inch 16:9 displays, but at this size, users get more vertical pixels to work with.
You can conveniently segment your screen into three same-size displays with a single ultrawide. At the same time, a dual monitor setup will hinder that use case with the bezels in the middle, not to mention the constant turning of the head from left to right, which gets very uncomfortable over a long period.
Having one giant monitor is also aesthetically more pleasing, and it keeps the desk clutter-free.