1. Little time
We are overwhelmed with information. Tons of distractions. When a person visits your page, you have a very short window of time to grab their interest and convert them.
https://convertica.org/how-to-reduce-cognitive-load/
2. More choice than necessary.
As soon as you overwhelm a user with unnecessary information—such as an excessive product selection or endless walls of text—forcing them to figure out why they should buy one item over another, you plunge them into unnecessary overthinking.
Hick’s Law states: «The more stimuli (choices) users are presented with, the longer it takes them to make a decision.»
3. Cognitive overload.
This frustration results in the user not understanding why they should choose one product over another. Because of this load, they simply leave the page, deciding to buy «some other time»—which may never happen.
4. Loss of trust.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0127680
This study cites an experiment showing that under heavy mental strain, people trust less and rely more on impulse decisions. On my landing page, however, my exact goal is to convince them to make the right choice. The more they doubt, the less they trust me. This was proven in the experiment above.
What to do:
1. Address all user questions as early on the page as possible. If they came to choose a product, provide that choice above the fold in a comparison table.
2. «We need to realize that our goal isn’t simply to give potential customers more options or products, but to ensure they have the single most relevant, important, and urgent option for them.» – Austin McCraw
3. If there are multiple choices on a product page, highlight the most popular one.
4. Allow users to sort or filter available options.
I can add from personal experience that a «WOW product» works extremely well—when one product stands out prominently on the page. That drives significantly more clicks, turning it into the sales leader.