They really do.
I have been involved with numerous tests in which we tested landing pages and offer pages with a single column and two or three columns.
Every time the single-column format wins.
Why? It isn’t much of a mystery. Using a single column helps control the eye-path of your readers. With one block of text, the reader is more likely to read from top to bottom, and absorb your sales message in the sequence you intended.
When your sales message is read from top to bottom in this way, it is going to significantly increase your chances of converting that reader to a customer or subscriber.
But when you add other columns, you are creating distractions. Your readers now have to make choices between one area of the page and another. Worst if all, a reader may be half way through reading your sales message and then be distracted by some visual element to the left or right of the sales text.
It is often tempting to add related or supporting materials in a separate column, but I would advise against it. If you have some great testimonials, for instance, don’t put them to one side, but include them within the main column of text. Make them an integral part of your sales message.