Maybe there is mismanagement, or poor decisions, or just not staying ahead of trends in the market - but putting millions of dollars into the pockets of the business owners is the intent of all businesses. Knocking that as "premature profitability" seems silly
They have the marketplace and the tooling already, just artificially limiting scale.
Becoming the number 1 player in that market could be profitable if said company could implement innovations that are difficult to replicate by others. But it's not the type of business where a network effect is going to shut out competitors. Customers will go to where they can get the best balance of price, quality, ease of use, and speed.
Spending a lot of VC funding selling dollar bills for 50 cents is not the only strategy, and it risks running out of money before getting to the promised land.
Running a profitable business doesn't mean you can't come to be the best in a market segment either. Profit can be reinvested in the business, and decisions can be made based on what makes sense for a sustainable business.
...What? Please explain why selling t-shirts online is a business where one winner will take all the market share.
Utilities are a natural monopoly. T-shirts are a commodity. There will always be thousands of sites selling them.
Or perhaps we need to consider the idea that it's actually OK for a company to not live forever. Threadless had a good run, made a lot of money for the employees and made a lot of consumers happy. It's not a failure if they don't continue to do that in perpetuity.