if this token do not get in exchanges listed and will be used just for own website then I do not see any possibilities why investors has to buy them. It can be then just interesting for gamblers.
You have a point, tokens should also be listed in other exchanges so that people will have more options where to buy this token. Also it will attract more investors to join.
Probably that is the way it should be so that investors can have many options to exchange the token. Also, gamblers will easily trade token in different exchanges without being hassled. Anyway, it's only my opinion let's just let the dev how they will deal with their token.