That's right, there are many other good ways to entertain yourself if you feel sad and feel like you're alone in life. Yes, it hurts to be left behind but it doesn't mean the end of the world for you, you have to get up and move on because there are many other opportunities waiting for you. Don't ruin your life with gambling, there are many other things you can do besides that.
I think loneliness is the reason why people want to gamble, it's too kill our free time. But when you feel sad and feel alone in this life, that means you're not in a good condition, so could do something stupid or may harm yourself. To overcome this, one should try to deal with himself, try to find a good way to fill your energy. For an introvert can try to take me time, while for extrovert can try to meet with other people.
This idea does make sense and the OP has given one of the headings that cause someone to enter and get involved in gambling. Everyone has experienced loneliness and whether they choose gambling or something else to occupy their time is a choice and it is also quite possible that circumstance could be the driving force behind why they choose gambling. I have one scenario where they are lonely and then open their gatget and accidentally find one of the promotions from an online gambling site and that's where it all starts, I don't think I need to continue this scenario because you can probably guess what will happen next.
So basically I think they can get into gambling in any way whether intentionally or not and one of them is this loneliness, the danger is when you try it and then you keep an interest in the activity. Yes usually this kind of scenario will be very likely to happen to those who are introverts and to minimize it they should try to be more open to the outside world such as playing with friends or relatives, it will be useful to distract you from gambling.