Is Teespring dead?
That is a question I get a lot...and the answer is simple...NO. They partnered up with the NFL they are going to be here for the long term. But for some people Teespring is dead because they do not innovate. Many marketers got into Teespring because they saw a quick and easy way to make money. Which is true but the market changes and you have to change with it.
So, the question still stands. Is selling T-shirts on the internet saturated? Watch this video by Mateen of Affengineer to find out:
I hope this answers your questions. The T-shirt industry is not dead and never will be until humans live on earth, that's my opinion.
So, diversify, look for new ideas and be creative. Do not get stuck one idea, design, or market. The opportunities are global.