Shopify or Ebay store?

I sell t shirts on eBay currently and they are selling well but at a slow pace. Is it worth me changing to a Shopify store and running ads. My worry is by selling on eBay i’m merely selling, not building a business. Does anyone have reccomendations?

PS the t shirts I sell are very niche and appeal to a certain type of folk, they’re not just generic t shirts.