I think the aspect of money involved is where the problem lies, honestly investing in stock is totally different from gambling because a person must be financially stable before going into stock and at the other hand gambling starts with little money. Some people can still view stock investment as a long term investment so reasons are much, one must be very careful making choice when it comes to investment because it might come with ups and downs when a person is not financially stable, let’s just accept the fact majority of people will choose gambling always.
And another fact why people may simply choose or spend more in gambling over investment and which is why the survey results that maybe even the case even outside America, people would spend more in gambling than investing in stocks, is simply because gambling's pacing is faster and less complicated compared to stock investments that needs different approaches of analysis to understand the market to minimize the risk of losing.
Also, gambling is a form of an entertainment, so majority may surely find it more enjoyable than trading, so there's that.