The STO can be called the most unSuccessful Token Offering method ever. It was used for a very short time and very few projects, and was not very popular. It was not very likely to be successful anyway.
Moreover, they were very cumbersome due to legal requirements.
Well, that could be argued, but I believe that the cumbersome legal requirements are what make STOs a safer option than other fundraising methods? I mean, we cannot forget in a hurry what happened with ICOs